A hot week and a hard lesson in coral heat stress

A sudden temperature change can place undue stress on your aquatic life…Dr. Foster & Smith Website

That is a quote from a  Dr. Foster’s article–and right now, it feels like the understatement of the century (hows that for an exaggeration).

toadstool and clownfishMy story starts a couple of weeks ago, when my tank experienced a relatively sudden temperature change that put stress on my tank and caused me to lose one of my favorite corals.While rummaging through the chaos under my tank (do you keep things tidy down there?), in the chaos before I left for vacation (there never seems to be enough time to get everything done before vacation), I must have inadvertently bumped the dial on my heater. I don’t have any other guess about how it happened.

At the same time, I purposefully dialed back the air conditioning in the house, knowing that we would be a way for the week (10 degree difference, maybe). Another instance where saving a few dollars (truly trivial) can cost you some money in this hobby.

Those two factors, along with the absence of an aquarium chiller are the recipe for a very melted toadstool coral.

In the summer time, we always have the air conditioning on, in the winter, we have the heat on. I know that may sound like possibly the most obvious statement in blogging history–but I mean this to say–my house is almost always 65-75 degrees Fahrenheit. So my aquarium water, by default, “wants to be” 65-75 degrees Fahrenheit, which is why I have a large titanium heater–but that means the heater is ‘working against the room temperature’ to keep the water warm. With the ambient temperature warmer and the dial cranked…the water temperature rose significantly.

If you’ve never had a soft coral “melt” and you’re wondering how you know it is dying (or dead)…you know…it was gross. I didn’t even have the presence of mind to photograph or video record it. There was just a flat film on the sand–I attempted to lift it out and what little flesh remained of the once massive toadstool leather flaked into a deathly snow and fell over the live rock and other corals. There was palm-sized piece that I was able to remove intact that smelled so rancid, I put it in a ZIPLOC bag and still had to take it right out to the curb. It wreaked of aquatic death and decay.

At the risk of sounding like a baby…I almost gagged…it was that foul.

Moving forward

I learned a few things about preventing coral heat stress, through this mistake, that I would like to pass along to you.

  1. Check your water parameters before you leaveangry-sun
    • Even if you’ve been in the hobby forever
    • Even if you did your water changes and ‘know’ they are good
    • Even if you’ve left the tank successfully 50 times before
  2. Mark your heater (if necessary) to highlight where ‘normal’ is, to make it apparent, at a glance if the dial moved
  3. Consider buying an aquarium chiller, even if you have never needed one before

Until now, I have never encountered a problem with my water being too warm, but when I got home from my vacation, the water was 90 degrees, my Toadstool had melted away (not literally), and the rest of the tank was exhibiting stress from the Hot Tub environment I had created.

An aquarium chiller could have prevented that.

I’m grateful that the Toadstool was the only loss. I’m not sure how or why that is. The other corals, while stressed, seemed to hold on alright. Maybe there was something else going on, in addition to the coral heat stress. It’s also important, and humbling, to note that even after all these years, I’m still making mistakes and still learning a lot. I think that’s what is so fulfilling about the hobby–our hobby–you never stop learning. If I ever sound like I have it all figured out…be sure to call me out on that.

So now, I’m on the market for a good aquarium chiller. I’m going to do a review of the chillers available on the market and report back what I learn.

Let me know if you have any recommendations.


  1. I’m so sorry about your toadstool. 🙁

    I’ve looked at chillers. They are incredibly expensive and impossible to afford one on my pay. 🙁 I was freezing bottles of water and dropped them into the tank. It was an on going battle to keep the temp reasonable. I even got up in the middle of the night to change the bottles out. Thankfully we got through it. If you see an affordable cooler, please let me know. Many thanks!

  2. I use a small fan that clips onto my refugium. It lowers the temp by 3 degrees when the light is on at night.

    1. Author


      Thanks for the comment and great suggestion. I’m going to check that out–based on what I’m seeing with aquarium chiller prices–your solution is undoubtedly a cost efficient way to lower the temperature.

      Thank you.

  3. Al why not get a controller? I have one and it turns my heater on and off. But I have the dial on the heater about a degree higher then the controller turns it off at. This came in handy when I noticed I knocked the temp probe out of the water. The redundancy save my tank. I didn’t even notice it until I saw that my controller was keeping my heater on 24/7.

    Another idea I heard about that I thought was neat is getting two smaller heaters. That way if one thermostat gets stuck it cant cook the tank.

    But controllers are way cooler. They have more buttons!!!!

    1. Author

      Thanks for the comment, Brooks–I love the idea of the controller-that’s a great suggestion. In terms of the redundant (underpowered) heaters, that’s another good idea. The worst that could happen in a malfunction is a cool tank. Thanks for the great suggestions! I do like the option that involves purchasing a cool new toy, with buttons!

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