Everyone loves adding fish, coral, and other invertebrates to their reef tanks. But before you can jump into that fun, you need to make sure you have your water on point. Reef tank water parameters are crucial for the health and well-being of EVERYTHING you add to the aquarium. And it can feel overwhelming. But armed with all of the information, you’ll find yourself testing and regulating your water conditions like a pro.
We’ll kick things off with the nine MOST IMPORTANT REEF TANK PARAMETERS before moving on to a few additional key components. And then, we can “dive into” how to test those conditions and manage tricky situations. If you want to focus on a particular water parameter, feel free to use the links below. Otherwise, you can read through the entire article and make sure you’re getting the hang of appropriate reef tank water conditions.
1: Alkalinity
Alkalinity is a complex concept to describe because it revolves around scientific explanations. As aquarists, we don’t care about the scientific definitions. We care about chemistry. Measuring alkalinity is a way to estimate the amount of bicarbonate available in the water. Bicarbonate is a vital molecular compound for the health of our reef tanks.
Why is alkalinity important in a reef tank? Alkalinity impacts the pH of the water (pH comes in as the sixth most important water parameter). Alkalinity’s role in affecting the available bicarbonate in your tank is also important because bicarb is one of the main ‘ingredients’ used to build coral skeletons. Therefore, you need to keep alkalinity in the appropriate range in a reef tank to ensure sufficient bicarbonate for your corals to grow.
Operational consequences of unstable alkalinity include coral tissue recession, stunted coral growth, and increased susceptibility to stress. Rapid swings or frequent corrections—especially when trying to “chase” a specific number—can shock corals and other sensitive invertebrates. Signs of alkalinity instability may include sudden coral distress, loss of polyp extension, or cloudy water from precipitation events.
Rather than aiming for a perfect number, prioritize keeping alkalinity stable within the recommended range and avoid making large, rapid corrections unless absolutely necessary.
Ideal Alkalinity for a Reef Tank
A practical alkalinity target for many reef tanks is about 7–11 dKH. Choose a stable level appropriate to your livestock and salt mix rather than chasing the edge of a broad range. That’s a pretty broad range. Perhaps more important than reaching a level within that range is trying to stay consistent once you find an alkalinity level that suits the inhabitants of your tank and is easy to maintain, based on your local water.
Although published target ranges vary, your aquarium won’t do well if the alkalinity drifts dramatically from day to day. So do what you can to maintain stable alkalinity. Even if you are trying to get your alkalinity up, you will want to do so very, very gradually to avoid shocking any of the animals in your system.
2: Ammonia
That same chemical in your glass cleaner that helps make your glass shine and stay streak-free? It’s inside your saltwater aquarium and comes in as the number 2 reef tank parameter to watch.
Ammonia occurs naturally as a byproduct of the organic waste breaking down in your tank. Ammonia gets into your reef tank when your fish pee (yes, normal biological functions apply to fish, too) and when food and other biological components (plants, live rock, etc.) rot. So it’s perfectly natural to see it in your tank. The problem is ammonia is toxic waste in your aquarium. In chemical terms, ammonia is a base or a basic compound – the opposite of an acid.
But while acids and bases are opposites, they cause a similar burn when they contact living things. The ammonia in your tank will burn your saltwater fish and corals and possibly kill them if high enough.
The good news is that a healthy, fully-functioning biological filter protects your tank by removing ammonia from your water. However, if you have detectable ammonia levels in your tank, it means your aquarium is too new (it has not fully cycled yet). Or you could have a problem with your biological filter.
- Undetected dead livestock (fish, invertebrates, or large snails)
- Overfeeding or sudden increase in organic waste
- Disruption of biological filter (e.g., cleaning filter media with tap water, replacing too much media at once, or power outages)
- Use of medications that harm beneficial bacteria
To systematically diagnose persistent ammonia:
- Check for missing or dead animals, especially in hard-to-see areas.
- Review feeding practices—reduce if overfeeding is suspected.
- Inspect filter function and recent maintenance—ensure media was not over-cleaned or replaced all at once.
- Consider recent changes such as medication use, power outages, or large water changes.
Ammonia can persist in “cycled” tanks if the biological filter is compromised or overwhelmed. Address the root cause, not just the symptom—removing dead livestock, correcting feeding, and restoring filter bacteria are key to long-term stability.
Ideal Ammonia Parameter for a Reef Tank
As another of the most important reef tank parameters, the ideal ammonia level for a reef aquarium is ~0 ppm. If your tank has fully cycled, there should be NO detectable levels of ammonia. Ammonia can burn your fish and corals. And at higher levels, it can be toxic. This is why there is no tolerance for this in a reef tank. The ideal ammonia level is ZERO.
3: Calcium
Have you seen a milk commercial on television promoting calcium for good bone growth? Well, fish aren’t mammals and don’t drink milk. (Now that I think about it, bringing up milk didn’t really help this story much) Moving on!
Calcium is an essential element in a reef tank for Small Polyp Stony (SPS) or Large Polyp Stony Coral (LPS) health. While they don’t have bones, they have bony skeletons made from calcium, and they get that calcium from seawater.
For that reason, calcium ranks third as the most important of the ideal reef tank aquarium water parameters and is especially critical for stony corals species like Bird’s Nest, Montipora, Acropora, Gonipora, Favia, Scolys, Blastomussa, Acans, and pretty much any other stony coral.
Ideal Calcium Parameter for a Reef Tank
The world’s oceans tend to have reef calcium levels between 380-420ppm (parts per million). That’s a fairly narrow range (around~400ppm). So, to keep things simple, I generally think of the optimal reef tank calcium level to be about 400ppm.
4: Nitrate
The fourth most important water parameter for you to monitor in your reef tank is nitrate. Technically speaking, the presence of low levels of nitrates in your tank could be considered a good thing. It means your biological filter is working. (News flash: you want that!)
In a properly cycled aquarium, bacteria convert nitrogen waste (often in the form of ammonia) into nitrite. Then other bacteria turn that nitrite into nitrate.
The problem crops up when your aquarium gets more crowded and mature. More and more nitrate gets generated, allowing the levels to climb. Small amounts of nitrogen in the nitrates get absorbed by certain soft corals or macroalgae. But it also acts as a fertilizer, boosting problem algae growth. (Nobody wants that!).
The animals in your tank will produce nitrates, but it also comes from the food you feed them, as well as from brine shrimp hatchery water. If you are feeding live artemia to your tank, you should filter the water so as to only introduce the clean shrimp to the tank.
Some invertebrates are intolerant of high nitrate levels. Their health will decline (adding even MORE nitrates) if left unattended.
Ideal Nitrate Parameter for a Reef Tank
For a reef tank, aim for nitrate that is low but detectable and, above all, stable rather than trying to force the reading to absolute zero. The useful range depends on your livestock, feeding, filtration, and test method. A tank dominated by fish or hardy soft corals may operate successfully at a higher level than a system with more nutrient-sensitive animals.
Watch the trend alongside coral color, growth, algae, and animal behavior. Use a reliable test method, confirm unexpected results before acting, and make changes gradually. If nitrate becomes undetectable or drops abruptly, do not keep increasing nutrient export automatically; reassess feeding and export so you do not trade a high-nutrient problem for a nutrient-starved tank.
Reducing Nitrates in Your Reef Tank
The fastest, most natural, and lowest-tech way to remove nitrates from your reef tank is to perform a partial water change.
However, to help keep your nitrates low on an ongoing basis, some aquarists employ the help of beneficial bacteria which eat the nitrates. They accomplish this via a process called carbon dosing. What is carbon dosing, you ask?
The short version is to allow beneficial bacteria to naturally grow in your tank. But you can give those populations a boost by adding carbon to your tank. Two common ways to do this are through the use of biopellets or vodka dosing.
Spoiler alert: The proper regimen for dosing vodka in the tank is NOT “one for the tank and one for me.” (Sorry to disappoint)
Populating your aquarium with soft corals, zoanthids and other corals that absorb nutrients from the water column will also help.
- Water Changes (Dilution): Simple and effective for small tanks or low bioloads, but becomes impractical for high-biomass systems or chronic nitrate accumulation. Frequent large water changes can stress livestock.
- Carbon Dosing (e.g., vodka, biopellets): Promotes growth of bacteria that consume nitrate, but overdosing can cause bacterial blooms, oxygen depletion, or outbreaks of cyanobacteria. Requires careful monitoring and gradual adjustments.
- Refugia/Macroalgae (Export): Macroalgae absorb nitrate and phosphate, providing natural export. Requires space and regular harvesting to remain effective.
- Deep Sand Beds & Denitrators: Support anaerobic bacteria that convert nitrate to nitrogen gas. Effective but can be difficult to maintain and may cause issues if disturbed.
Key Point: Water changes dilute nitrate, while biological and chemical methods export it from the system. Rapid drops in nitrate can stress sensitive livestock, so always reduce levels gradually and monitor livestock for signs of stress.
5: Nitrite
The fifth most important saltwater aquarium water parameter is nitrite. No, that is not a typo. Nitrite and nitrate are two separate and important compounds to monitor in your water. Though they ARE related to one another through the nitrogen cycle.
Nitrite is an intermediate by-product produced by your bacterial filter as part of the nitrogen cycle. In your filter, bacteria convert toxic ammonia into less toxic nitrite before the second group of bacteria converts the nitrite to nitrate. (See? It all makes sense in the end)
Ideal Nitrite Parameter for a Reef Tank
For a very brief period of time (a few days, MAX) – say, while you are cycling your tank – you look for the presence of nitrites in your tank. This provides evidence that naturally occurring, beneficial bacteria have colonized your tank.
Other than that, you want your nitrites to remain as close to ZERO as possible. If you see any level other than zero while you’re testing your water, it’s a symptom that A) your biological filter has crashed or B) it can’t keep up with SOME large source of ammonia (say, a dead fish you haven’t located yet).
6: pH Level
I won’t bore you too much with the scientific definition of pH. It’s a long, drawn-out explanation that revolves around hydrogen ions. The pH scale is logarithmic, meaning that 8.0 is MUCH farther from 7.0 than you think. The way I think about pH is this: the pH level tells me how acidic (or not acidic) the water is.
The scale reads from acidic on the low end to basic on the high end. The pH is essential to the chemistry of your reef tank, which is why pH ranks as one of the most important reef tank parameters.
- CO2 accumulation in the room or tank (from poor ventilation or high bioload)
- Photosynthesis and respiration cycles (pH rises during the day, falls at night)
- Low alkalinity, which reduces the water’s buffering capacity
To diagnose and address persistent pH problems:
- Increase aeration (e.g., adjust skimmer, add surface agitation, or open windows to reduce CO2)
- Check and maintain alkalinity within the recommended range
- Avoid quick-fix pH buffers; these provide only temporary relief and can destabilize other parameters
Addressing the root cause—such as improving gas exchange or correcting alkalinity—is more effective than using chemical pH adjusters.
Ideal pH Parameter for a Reef Tank
The ideal range you want to aim for is ~8.1-8.4 for a healthy saltwater aquarium.
While the absolute pH is important, it is perhaps even more important to ensure it remains stable. Dramatic swings in pH can cause problems for your livestock. If your pH rises above or falls below that range, take your time correcting the underlying cause over hours or days (depending on how dramatic the difference is) to avoid shocking your fish, corals, and other invertebrates.
7: Phosphate
The seventh most important reef tank water parameter to monitor is phosphate. Phosphate occurs naturally on reefs, but the concentration varies with location, depth, biological activity, and the testing method used. In a saltwater aquarium, too much phosphate can become a big-time trouble-maker.
In your saltwater aquarium, phosphate acts as a fertilizer for algae, And if your tank is like mine, you probably don’t have the same types of algae-eating controls as a natural reef.
Ideal Phosphate Parameter for a Reef Tank
Determining the ideal level of phosphate for a reef tank is tricky. Since it fuels problem algae growth, you want to keep it low, but phosphate IS also a nutrient. Aim for a low but measurable and stable level that suits your livestock and nutrient-export strategy rather than chasing a universal number or an absolute zero.
Use a reliable low-range test, track the trend, and confirm an unexpected result before changing course. Rising phosphate together with increasing algae may justify more export, while an undetectable reading paired with pale or receding corals may mean you have pushed removal too far. Make adjustments gradually and avoid abrupt swings in either direction.
If phosphate is consistently trending too high for your system, you have a couple of practical export options:
8: Salinity
The eighth most important reef tank water parameter is salinity. When I say that the salinity of the reef tank water is important, I’m referring to the amount of salt in the saltwater. (I know, crazy concept) But salinity is difficult to measure directly.
One way to measure the salinity of the water is to completely evaporate a liter of saltwater and weigh the salt left behind. That would be your salinity. However, it’s not the most practical way to handle things with a reef tank.
Luckily, some super-smart people came up with a few super-easy ways to estimate salinity.
When the salinity of the water changes, two other things fluctuate at the same time:
- Density
- Light refraction
So, aquarists use a hydrometer to measure the water’s density (specific gravity). We also use a refractometer to measure the angle of light refraction to estimate the salinity.
The most common type of hydrometer used in this hobby is called the swing-arm model. It looks like this:
You measure the salinity by submerging the device and filling it with your aquarium’s water. The arm is carefully calibrated to float and point at the water’s corresponding specific gravity and salinity.
The other way of measuring salinity is with a refractometer.
Refractometers are more precise and less likely to fail. However, they require you to occasionally calibrate them to maintain the desired precision. This is what a refractometer looks like:
You have to have salt in the water to create salinity. (Sounds reasonable, right?) So most of us make our own seawater with a salt mix.
Ideal Salinity Parameter for a Reef Tank
The salinity of the ocean comes in at ~ 35 g/L (using the evaporation method). But hobby aquariums measure the specific gravity of the water because of the ease of the measurement. Ideally, you want to keep your aquarium reef at a specific gravity of 1.025. This is the simplest way to ensure the salinity replicates the salt concentration of a natural reef.
9: Temperature
The ninth most important reef tank water parameter is temperature. The majority of animals we keep in our tanks come from tropical reefs, and tropical reefs tend to have a stable temperature between 73 and 84 degrees Fahrenheit (22 to 29 degrees Celcius).
If you live in an area where the ambient temperature matches that range…Well, I’m a bit jealous and hope you’ll invite me over to hang out very soon. If you don’t live in an area with a steady tropical temperature, you will need equipment to keep the aquarium temperature in the right zone.
An aquarium heater is required for just about any aquarium. Unfortunately, most of us live in houses where the daily temperature is lower than the ideal values listed below. The aquarium heater raises the water temperature and helps keep it from falling below optimum levels.
If you live in a warm climate, where the temperature gets above the ideal range, you may need an aquarium chiller.
Ideal Temperature Parameter for a Reef Tank
Since most of what we do is intended to recreate the natural environment our animal friends come from, it’s no surprise the ideal recommended temperature for the saltwater in your reef tank is the same. A narrower 76–80°F (24.5–26.5°C) is a practical starting range for many tropical reef aquariums. Confirm the needs of your species and prioritize stability over chasing one exact number.
That’s a pretty broad range, and you might experience some challenges with finicky species at the extremes. The most commonly provided advice within that acceptable range is to keep your aquarium temperature around 78-80 degrees Fahrenheit (25.5-26.6 degrees Celcius).
As long as the temperature of your saltwater aquarium is in this range, keeping the temperature consistent becomes more important than the actual value itself.
Other Important Reef Aquarium Parameters
Now, let’s take a moment to review three other important reef tank parameters. While they don’t appear in the top nine, they’re still important for maintaining a healthy reef environment. And you’ll want to make sure you don’t neglect them:
There are a couple of reasons those three reef tank parameters didn’t make the cut. First is that, well, the list of the nine most important items stops at nine. (Everyone learned to count on Sesame Street, right?) You have to draw the line somewhere, and I did my best to prioritize the top 9 based on my own knowledge and experiences.
Next, these parameters are not as easy to measure or moderate through supplementation and water changes as the major items in the top nine. Please don’t read this as me saying that these three elements are not important to reef coral biology because they ARE. The critical factor is not that these are irrelevant biologically, simply that they aren’t as practical for the average aquarist to focus on.
As far as I can tell, the science supporting the dosing of these trace elements in a reef aquarium is inconclusive. So, I took them off the list. No sense measuring something you don’t intend to act upon.
Iodine
As a trace element, iodine holds importance to several macroalgae, shrimp, and coral species. Still, because natural levels are so low (0.06 ppm), it is difficult to test and maintain these levels with standard test kits. As such, I DON’T recommend dosing iodine as a supplement with the intent to keep levels consistent with natural seawater.
It was once speculated that iodine was necessary to keep pulsing xenia alive, but later that information was refuted.
Observational and sometimes speculative information like that makes it challenging for an aquarist to know what to focus on. You want to avoid doing more harm than good in trying to create the ideal living conditions.
Ideal Iodine Parameter for a Reef Tank
The ideal concentration of iodine in a reef tank is 0.06ppm. However, because those levels are so low, testing would be complex. Also, the benefit of maintaining that level so precisely is unknown. At the same time, the risks of adding too much (toxicity) ARE known. Therefore, it is probably best to resist the urge to monitor and adjust your iodine levels manually. Instead, buy a high-quality salt mix that roughly approximates the natural levels of the ocean and stay on top of your water changes.
Magnesium
Magnesium is an important ion and the third most abundant in seawater. For the advanced reefer, it plays a major role in creating some of the problems faced. However, for the vast majority of us, this tremendously important ion is naturally present in such large amounts. As such, it’s probably not worth worrying about it on an ongoing basis.
As such, I put it in the “Nice to know, but don’t need to worry” bucket. At least for right now. If you’re already an advanced aquarist, then you may want to dig a little deeper.
Ideal Magnesium Parameter for a Reef Tank
The best magnesium level for a reef tank is likely consistent with the range found in the ocean, approximately 1285-1300ppm. Levels that drift significantly outside of that range can cause problems, including causing issues with other parameters such as calcium. But until you reach an advanced level of sophistication – or if you’re otherwise experiencing problems with your water quality and need to rule it out as part of the problem – you may be able to let sleeping magnesium lie and focus on the nine most important water parameters.
Strontium
Strontium is a bit of a controversial supplement in the saltwater aquarium hobby. (As controversial as something like strontium supplementation could be) I just let those words wash over me for a moment and pictured a hotly debated strontium controversy between two uber fish geeks. Okay, back to the article…
If you want to learn more about strontium than most chemists (slight exaggeration there), you have advanced aquarists who’ll do a fantastic job. (By the way, the author states that typical ocean levels of strontium are 8 ppm).
Ideal Strontium Parameter for a Reef Tank
Basically, this is another ion that belongs to the realm of advanced aquarists. However, if you geek out on water quality, you want to see your strontium level at ~8 ppm.
Recap
So those are the nine most important marine aquarium water parameters, with three other important items thrown in for fun (but probably not worth a lot of your time and effort). You CAN learn more about them, or you can zero in on them if you’re having serious problems and already ruled out your top nine.
Test Your Reef Tank Parameters
Okay. So, you know where to focus your attention when it comes to water. But what do all of those numbers MEAN, and how do you figure them out?
Equipment for Testing Reef Tank Parameters
You need to test your aquarium water to check that the levels remain within healthy and suitable ranges. Choose test kits whose range and resolution fit the parameter you are measuring, and use the same reliable method consistently so you can compare results over time.
To tackle four of the most important reef tank aquarium water tests—ammonia, nitrite, nitrate, and pH—a saltwater master test kit is a practical starting point. Using one kit, you can test four of the big aquarium water parameters in a few minutes. Compare the kit’s measurement range and readability with the needs of your aquarium before choosing one.
For phosphate and calcium, I have generally used individual test kits.
- Calcium test kit
- Low-range phosphate test kit
- Follow test kit instructions carefully and use consistent timing, lighting, and technique for each test.
- Calibrate or check test kits regularly, especially for digital meters or refractometers.
- If results are ambiguous or seem inconsistent with livestock health, retest, use a different brand, or consult a local store for a second opinion.
- Always interpret test results in the context of livestock behavior—healthy, active animals are often the best indicator of water quality.
No hobby-grade test kit is perfect, so consistency in your testing method is key to tracking trends and making informed decisions.
Equipment for Measuring Reef Tank Parameters
For salinity, a calibrated refractometer is a practical choice. A swing-arm hydrometer is another inexpensive option, but check it periodically against a trusted reference because bubbles, residue, and wear can affect the reading. You can find more options in the equipment guide.
For temperature, use a reliable digital aquarium thermometer and periodically compare it with a second thermometer.
Equipment for Maintaining Aquarium Water Parameters
High-quality reef tank water starts by using a high-quality reef aquarium salt mix. To keep your water parameters in the ideal range, you may want to have a protein skimmer installed in a sump with a refugium, a calcium reactor, and reliable heaters, and/or a chiller.
Biological Filtration to Keep Your Water Pure
In a marine aquarium, the biological filter will help keep your water in tip-top shape. Helpful bacteria that live on and in the live rock, live sand, and even on the aquarium glass will help remove toxic ammonia from the water and replace it with much less toxic nitrite. Then, the second group of helpful bacteria converts that nitrite into nitrate.
If you choose to add macroalgae to your sump or even display them in the tank itself, the macro will actually pull phosphates, silicates, and nitrates out of the water, as well.
If you want to take this biological filtration one step further, you can add a deep sand bed to your tank or refugium. The deep sand bed creates a low-oxygen environment at the bottom of the bed where the third type of beneficial bacteria can grow.
These natural, biological methods of keeping the water clean will help you keep the water in your home reef in a suitable range for growing the most amazing corals.
Troubleshooting
If you’re encountering problems with water parameters in your reef tank, then you can check this list of the top troubleshooting issues. Odds are you’ll find some of the top problems that can wreak havoc with water conditions.
- Confirm Test Results: Retest using a different kit or method if results are unexpected or inconsistent with livestock health.
- Observe Livestock: Look for signs of stress, disease, or abnormal behavior.
- Review Recent Changes: Consider recent additions, removals, equipment changes, or dosing adjustments.
- Check Equipment: Inspect heaters, filters, skimmers, pumps, and auto top-off systems for malfunctions or settings changes.
- Investigate Contamination or Decay: Search for dead livestock, decaying food, or foreign substances.
- Implement Targeted Interventions: Address the root cause—remove dead animals, correct dosing, repair equipment, or perform a water change as needed.
Example: If you detect a sudden ammonia spike, confirm with a second test, look for missing fish or invertebrates, check for recent filter cleaning, and review feeding practices. Address the cause before taking corrective action.
- Regardless of whether you spend $7 on an API test or ~$20 for a Salifert test kit, take measures to ensure your glassware is clean (and not contaminated) and that you perform the test according to the included instructions. If not, you could get false readings on your reef tank parameters.
- There is no substitute for OBSERVING your reef tank and visually determining if the data point from your test kit is consistent with what your eyes see. Unfortunately, test kits can and do fail.
- If you get a really high nitrate reading, but your tank tells you otherwise, do a water change. But also get another kit to verify it isn’t a false reading.
- To help keep your water quality as high as possible, you may want to purchase a high-quality protein skimmer.
- If water quality isn’t your problem, but you have some sort of pest, parasite, or infection, you may need to move your sick animals to a hospital tank and treat them with aquarium medication instead.
Disclaimer
A big disclaimer: I’ve listed GENERAL reef tank parameters.
Specific individual species you acquire for your tank may come from an environment that differs from these generalities and may, therefore, require specific care. But, again, it is up to you to research the husbandry needs of the animals you want to keep to know if their needs differ from the standard water parameters.
And if your animals require specific aquarium water parameters? Do your best to meet those standards. Or steer clear of those animals.
For More Information
Thanks for checking out this article about the most important reef tank parameters! Continue the journey to read, learn, and explore by checking out these books.
Want to keep reading and learn some more about the most important reef tank aquarium water parameters?
- Alkalinity
- Ammonia
- Calcium
- Iodine
- Magnesium
- Nitrate
- Nitrite
- pH
- Phosphate
- Salinity
- Strontium
- Temperature
The Inspiration for This Ideal Reef Tank Parameters Article
This article about the most important reef tank parameters was inspired by a short blurb in an old Doctors Foster and Smith’s catalog titled “Ideal Marine Aquarium Water Parameters: Key to Continued Inhabitant Health.” The article was short, to the point, and communicated a lot of information on a single catalog page.
The aquarium water parameters listed on this page are adapted from Wikipedia, Dr. Foster and Smith, and Advanced Aquarist. I cross-checked the information in their table with other reputable sources. But it also created a few unanswered questions in my mind. Questions like:
- Which parameters are the most important?
- How close to ‘ideal’ do you need to keep the water parameters in your own aquarium without causing problems?
Hopefully, with this piece, I managed to cover the ideal reef tank water parameters and which reef tank parameters are most important.
What do you think? Are there any saltwater parameters more important than these nine? If so, please leave a comment below.
Hi, I’m a new reefer and know nothing yet. But I wanted to ask about your recommended phosphate level. You said .2PPM. Did you mean .02? .2 is a lot higher than I’ve seen recommended elsewhere.
Hi Dave, thanks for the great question. Unfortunately, the answer, like many of the ‘facts’ in this hobby, is that it depends on a few things. Phosphate is a bit tricky. It certainly does cause issues. It affects calcification in stony corals and is often a major contributor to algae blooms.
But is is also an important nutrient. Running it too low can also cause other problems in the reef tank.
If you’re experiencing problems with algae and your levels are high, then your phosphates are probably too high, and it is worth chasing lower numbers to help address the problem, probably regardless of the results you see from your test kit.
However, the opposite is also likely true, if your tank is thriving and your phosphate levels are between 0 and 0.2 ppm, you don’t really have a phosphate problem at all.
Another reason it depends is considering how practical it is to measure ultra-low levels.
The most popular test kit only measures down to 0.25 ppm. So if you get a result that looks like ‘zero’, it could be anywhere between 0 and 0.25 ppm. So the advice here is pretty much to stay ‘undetectable’ by that test.
Hanna instruments does make an ultra low level instrument, but that instrument is $60, just for phosphate, and the accuracy from the manufacturer is +/- 0.04 ppm +/-4% of the reading if you measure at 77 degrees Fahrenheit…so you can’t even reliably measure 0.02 ppm because the margin of error is 2x the reading. Stated another way, even if you measure 0 on that instrument, you could still be as high as 0.04 ppm. A 0.02 might be an 0.06, etc. Those instruments also have to be carefully calibrated. Not saying we’re not all capable of that, but it adds to the potential error in trying to measure a really small thing.
There is also a trend these days of trying to run tanks a little ‘dirty’ vs. some of the super-clean trends from several years back, purposefully, among some of the leaders in growing SPS corals. In my experience, the other corals are usually not as demanding as those high-end SPS.
I do think it’s accurate and reasonable to point out that my estimate here is on the high-side of most of what is written on the topic, even those who talk about running purposefully ‘dirty-style’ tanks, and would therefore say it’s also reasonable to aim on the low side of <0.2 ppm, if you can get there and keep it there, or if you’re planning to keep the most finicky corals, and/or if you’re seeing any ill-effects from phosphates.
The recommendation on this page is also prone to some bias based on what’s easily/reasonably measured by an average aquarium owner (like myself) vs. perhaps being tied to an empirical truth, so perhaps I do need to do a bit more research and updating.
I really do appreciate your question. I will dive into this topic a bit more as well, to make sure this article has the most accurate and up-to-date information.
Thanks again.
Regards,
Al