Size of CUC


Staff member
RC Mod
clean-up crew, that is.
Yes, you do need more for a bigger tank...but! for a NEW tank you don't need more than a few. Why? Because you can't feed them yet.

The 'cleaner packages' the stores sell are nice for a refurb in an older tank: yes, there is attrition, and tanks increase in crud that the CUC can help you with.

But understand what a CUC actually does. They're not there to eat your waving fields of green algae (fix your phosphate level instead). They're there as undertakers, if something dies, as things will, and meanwhile they have to eat, so you have to factor them into your feeding, without overcharging your tank ith invisible nutrients---things you can't see, but that are floating about for microlife.

Your tank is not a box filled with pure water and only fish. It has a pretty active life under a microscope, creeping crawlies and bugs of all sorts, and it SHOULD be that way. Your shelly CUC is only the top layer of that activity that goes on mostly unobserved on the microscopic level.

A mature tank does have layers and layers of activity, from honking big snails to bristleworms (yes, they're good: a dollar a worm if you have to buy them.) and on down to copepods, amphipods, (look like swimming rolly-polies) and a few slightly pesty species, and on down to the microscope.

But developing that takes time. So start with a few simple crabs (some are bad mannered: go for scarlets and little blue-legs---and provide them enough spare shells so that they aren't desperately seeking snail shells: you wouldn't like a pair of size 5 pants, eh? So give your crabs some alternatives to snail-murder and everybody will live long and prosper.

For snails, avoid the simple pointy ones: they're not built for crawling on sand, and literally fall over and become crab food because they can't get a grip on the sand. Go for ceriths and snails with a classic winde-ey shape. And only a few at first, like maybe 3 of each for a 30 gallon tank, and work your way up to more as your tank begins to get that lived-in, scruffy look.

Getting an under-sand cleaner is a good thing: gobies that burrow can do this, as can bristleworms. I don't trust cucumbers: some are toxic if demised, and they are somewhat delicate. Just---if you notice your CUC is not keeping up with the debris, you could need more, but don't go crazy, eh? Also don't worry if your CUC steps on your corals---they're llight, and don't do any harm.



Crab Free Zone
Premium Member
Wise input.
Every week, LFS love to tell people to buy these large CUC packages to newer reefers indicating that these guys will keep your tank clean.
Great husbandry and rock solid chemistry will keep your tank clean.
I fired all my crabs 3 years ago. They quickly figured out that every day, free tasty food falls from the sky, forget algae, we want meat!

I have not had to replace any snails in three years now.

Interesting write up.


Staff member
RC Mod
As a side note, I got some fighting conchs (little ones) years ago. Yes, they do burrow, but you'd think you'd see them again. Still, I have a LOT of rockwork.

Well, while inspecting my tank this week, some 2-3 years after I bought these elusive little snails---here's one surfacing. Spent maybe 10 minutes sorting itself out, getting clean. Then it dived back into the substrate. Back to work in the underground. I've got one scarlet crab I know is over five years old. And some real tiny ones that live in cerith shells and have never outgrown them. I'm rather fond of hermits, as some people curse them, but then I've never gotten anything on the larger side: the scarlets are about as large as I am willing to accept in a crab. The other, non-hermit types, are a no with me, ever since, in a previous tank, the much-praised mithrax emerald crab took a healthy nip out of my mandarin's finnage---and it was not after the finnage, no: that dastard was after a whole fish dinner. Sally Lightfoots likewise: cute as they are, the sight of an adult the size of a dinner plate turned me right off that species. If I met that fellow coming down the street, I'd scamper out of the way myself.


Crab Free Zone
Premium Member
Yup, I’m sure there crabs that are ok, just there’s so many species (greater than 4000 I think) I cant tell the difference between good and bad. Years ago now, My red legged hermit (or at least I thought that was) was somehow able to sneak up on my male black occ which at night kinda hovered just above a rock tip, and grabbed it by the belly. I thought I was dreaming. I intervened but to much initial damage.

I am glad that I’m not the only one that had to learn the lesson.

From that date going forward, I will never add a crab.
The result from that 5 years or so later is that mysterious disappearances ceased....hum....ya think.



Well-known member
The CUC for my 120DT consists of a handful of assorted snails - mostly ceriths and nassarious, a single scarlet reef hermit that I've had for well over 20 years, and all the bristle worms the tank will support. IMHO, the huge CUC recommended by most online vendors are just a waste of $$$. By the time 98% of them die from starvation, you'll end up with, lemme think, a handful of assorted snails, a reef hermit or two, and a bunch of bristle worms.