Clean up crew: is it worth it?

The job of a clean up crew (CUC), in a saltwater aquarium, is to keep the tank clean by eating the leftover food, algae, and detritus in your tank. A clean up crew typically consists of a mixture of crabs, snails, and the occasional shrimp.

are clean up crews worth it?
Hermit crabs are popular CUC invertebrates
This guy hitched a ride in on live rock but is now part of the CUC

do clean up crews do more harm than good?

But the use of clean up crews is controversial in the hobby.

  • The argument in favor of CUCs is that they provide valuable service within the tank of removing food and detritus waste that would otherwise pollute the tank. CUCs also graze on algae, keeping it in check.
  • The argument against CUCs is that they add unnecessary bioload and waste to the tank, essentially straining the system more than it would be if the cleanup crew wasn’t there in the first place.

Over the past year or so, I’ve watched as ‘the herd thinned out’ (clean up crews don’t really travel in herds) in my tank. Personally, I’m conflicted and don’t know whether I should replenish my crew. But before I decide, I thought it might be worth belaboring the point here for a few minutes. I hope you don’t mind. The reason I’m conflicted is that I think both sides are right. Clearly, the clean up crews I have had have spent a lot of time and energy moving around my tank eating stuff I would otherwise have to clean out myself. But I honestly have no idea if they do more harm than good. I don’t even know how you would prove that hypothesis. But why let facts and proofs get in the way of a good (or even mediocre) story. Here is my thought process:

Where’s the beef?

In grappling for a model to help figure out my CUC dilemma, the best I associate the CUC dilemma with–and the best I could come up with was cows to a farm. The cow eats grass (or corn and pink slime, depending on where the cow is…but that’s a tangent) all day, every day. Theoretically, the cow turns some of that energy into the steak (mmm….steak), and some of that energy into manure and some of that into the energy it takes to turn that stuff from one thing to the other. But, all things being equal, if the grass is analogous to the algae and detritus in a saltwater tank, I feel pretty confident that the cow, as a ‘grass remover’ would be a good addition to the farm. Sure, it would make a lot of manure too, but it would clear a pasture of grass, right? I have to think the general premise would hold true for the crew, right?

Where did they all go?

But if you have ever had a CUC in your saltwater aquarium, you know that the crew starts losing members after a few days. The snails and crabs just start to vanish. So clearly the dead animals that get lost in the tank could potentially pollute the tank and cause more trouble than they are worth, right? I think the unaccounted for decay tends to be the big deal-killer when it comes to the decision about whether or not to add the clean up crew. Clearly, the cow doesn’t just decay out of the pasture–I would think that would foul things up a bit there. Hmmm…maybe the model doesn’t work.

Balancing act

Then again, isn’t this is where the law of conservation of matter comes into the mix? The crab or cow or snail (wait, what are we talking about again?) could only be made up of the carbon and nitrogen and other elements it ate before being added to the tank and since being added to the tank (minus whatever energy was lost in the conversion, right?)

So then even in the situation where the animal does decay without being removed from the tank, the net contribution to waste has to be less than what it consumed, unless it died quickly after being added to the tank (which some undoubtedly do).

But I can’t get past the fact that the cow doesn’t just decay on the pasture. The cow gets removed from the pasture–harvested essentially, the same way we would harvest chaeto from our refugia or algae from an algae scrubber. So is the cow really the right model? Is the answer that clean up crews DO make a difference, you just have to take them out before they die? Would anybody do that?

It seems a bit heartless to me to euthanize these animals, but is it really that much different from the way people use chaeto in a refugium or an algae scrubber?

What do you think? Are Clean up crews worth it or do they create more pollution than they clean up? Would you ever consider harvesting your crew to eliminate the risk of them dying in your tank? I’m not advocating it, just wondering if it solves the problem and if anyone would do it. Let me know what you think.





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