Adding clean up crew to your marine tank

Taking the mayhem out of marine fish keeping


Adding clean up crew to your marine tank


Under normal circumstances, once your tank has cycled, the beautiful white sand, gleaming rock and crystal clear glass has succumbed to a green halo of algae, a brown dusting of gunk, maybe a light red coating of cyanobacteria and a general look of dirtiness.


This is normal and is simply the tank starting to balance its parameters and generally sorting itself out. Cyanobacteria in particular, is often associated with an imbalance in parameters and chances are your tank will suffer from it at some time during its life.


Once your ammonia and nitrite readings have stayed at 0 for a period of time (I would suggest a minimum of a week) after adding some organic matter to the tank (like a pinch of frozen fish food) it’s time to start thinking about your clean-up crew.




Clean-up crew (or CUC for short) is the term given to a group of critters that will help to clean up your tank, either by scavenging on tiny pieces of leftover fish food or spending their lives wandering over your live rock grazing algae. There are also some species that reside in the sand bed, these can be very useful at helping to turn the sand bed over making sure no compact, dead spots start to develop.


Generally the species referred to as clean-up crew are the snails, conches, hermit, and some other, crabs and shrimps. There are also sea hares (a type of slug) and nudibranches but these tend to be employed for more specific, and often more serious, cleaning duties and need a little extra care with their husbandry. As would be expected different species carry out different duties so a combination of all them tends to work well.


In the early stages after your marine tank has cycled you should consider only adding a proportion of your final CUC stock as the tank will still be unstable and ultimately they could starve to death as they graze down the algae but because your water parameters are improving no algae grows back to replace it.




Snails are arguably the most important members of your clean-up crew, various types will make it their life long duty to devour various types of unwanted algae. The most common you will see for sale tend to be:


Cerith snails – useful for the green, slimy type of algae you get building up, particularly on the glass, they are also reported by some to help clear diatoms which are often responsible for the brown dusting you get in new tanks over the sand and rocks. Cerith snails can also help to clear up left over food and fish waste.


Astrea snails – useful for grazing down hair algae and as Cerith snails have been reported to help with diatom blooms.


Turbo and Trochus snails – tend to be favoured for helping to keep hair algae in check, these useful additions to your clean-up crew will also help to clear the film of slimey, green algae that builds up on the tank surfaces. Some turbo snails can grow to a fair size so you need to be careful if you have any invertebrates in your tank that are likely to get bulldozed off their ledges.


Nassarius snails – these are a personal favourite of mine although probably better suited to a more mature tank. They bury themselves in the sandbed helping to keep it turned over and minimising the risk of compact and dead spots building up. They are great little hoovers, cleaning up general detritus and fish waste and can help to control diatoms. They are usually hidden until they smell food when you will see their ‘snorkles’ pop up out of the sand bed soon as they unearth themselves and embark on their cleaning duties.




Many of the ‘CUC’ packs offered for sale will include hermit and sometimes mithrax crabs. Whilst I wouldn’t have a tank without them (they are one of the most amusing things in my tank) you need to treat them with caution. All of them pose a risk in one way or another. They are great little scavengers and you will see them picking through bits of algae or invisible bits of detritus all day long. All crabs, however, are opportunistic and if they go hungry or are able to catch a tank inhabitant they will attempt to nibble on anything they can get their pincers around. I am constantly picking hermit craps off my sps colonies and whilst I haven’t noticed any real damage I’m pretty certain the corals aren’t ever so happy with the arrangement.


It’s also worth pointing out that hermit crabs are quite vain and like to change their shells frequently. If there are not enough available empty shells knocking around the tank they won’t think twice about stealing someone elses, sometimes to the point of killing its occupant. They are also quite able to remove a snail from its shell resulting in the rapid demise of your snail population.


Some of the smaller hermit crabs are considered safer than others. The blue legged reef hermit, the red legged reef hermit and the scarlet reef hermit are all readily available and less likely to cause carnage than their larger cousins, but again, I stress, use any of them with caution.




You will often see shrimps recommended as clean-up crew and indeed included in the ‘janitor’ packs you can buy. Whilst all shrimps are great scavengers they too need to be treated with caution. The three common ones are the cleaner, peppermint and blood shrimp. None should be introduced until your tank has settled down for a few months as they are very sensitive to changes in water parameters.


Cleaner shrimps are great fun and do just that, clean, everything. They are also very excitable and almost do backflips when food is put in the tank. Whilst amusing to watch they can cause problems with some corals, particularly lps corals as the shrimps constant attention can cause them to close up and retract meaning they miss out on their meal. There is also nothing more annoying than painstakingly target feeding 30 individual heads on, for example, a sun coral, only to turn away and find your cleaner shrimp has stripped it of food in two seconds flat. I have spent far too many hours of my life standing guard over lps corals with a turkey baster literally blasting cleaner shrimps with a jet of water should they get too close.


Cleaner shrimps will attempt to set up a cleaning station as they would in the wild, whilst some fish appreciate the attention and will actively seek them out others seem either annoyed by them or frightened of them. Whilst I do think cleaner shrimps are a great addition to a reef tank it’s possibly better to get familiar with your new marine tank and its inhabitants before introducing something that can cause a bit of bother.


Blood shrimps are far quieter and tend to keep themselves to themselves a lot more. They are incredibly beautiful with their scarlet, white spotted bodies and pure white socks. They are also cracking scavengers but are shy and tend to hide away quite a bit.


Peppermint shrimps tend to employed not only as scavengers but to help eliminate the tank of a pest anemone called aiptasia. They can be hit and miss, if they are well fed on bits of left over fish food then they will happily ignore every aiptasia in the tank. Sometimes, however you can get lucky and they will almost obliterate the whole population. Again these shrimps are more suited to an older tank and should be treated with caution. If they go hungry they can pick at some coral polyps.


Try to avoid the ‘camel’ or dancing shrimp, they are nasty little things that can really pick on corals to the point where the coral may die.




Urchins, again are more suited to older marine tanks and can cause some problems but they can also be useful at keeping the rocks free of algae. They graze the rocks by using a harsh scraping action which can also help to free older rocks of corraline algae. Whilst most people are keen to see their rocks turning pink with corraline it has been suggested that it can reduce the porosity of the rock over time which can lead to reduced filtering potential.

I would suggest keeping to the smaller urchins like the pin cushion or tuxedo, you will also see long spined urchins for sale but these can be nightmare bulldozers and their spines grow long. They are also very good at finding your hand in the tank and positioning themselves just close enough so you can experience the sharpness of their spines first hand. This can lead to a sharp retraction of said hand, leading to hitting ones elbow on the overhead light unit, leading to various expletives being announced in rapid succession – stick to tuxedos…..


All of the above mentioned species are, of course suited to reef type set ups. If you’re going for a FOWLR then chances are your stocking with more predatory species of fish which will probably make a meal of your clean-up crew. In this case you either accept that you, yourself (and some sort of scrubbing implement ) are the main constituent of the clean-up crew or you could try a couple of the larger hermit crabs. These things are like bulldozers though so make sure your rockwork is stable!


Acclimatising your clean-up crew.


Clean-up crew are invertebrates and as such are very sensitive to changes in water chemistry. I would suggest a slow, gentle acclimatisation lasting around forty minutes for crabs, an hour for shrimps and up to two hours for snails, the latter being very sensitive to changes in their water which can lead to long term problems. They may wander around the tank for a week or two looking great then start to die off over the next few weeks, due to the damage caused by inappropriate acclimatisation.


The best way to acclimatise your invertebrates is by using the ‘drip’ method, this is gentle and prolonged thus reducing any potential for shock when introducing the creature to your tank.


In brief, you will need a bucket, some airline and an air valve (I also find a couple of clothes pegs come in handy.

Put the critter and the water it travelled in into a clean bucket next to the tank that can hold about three times the amount of water that’s in the bag. Start a syphon with the air line running from the tank into the bucket. Use the valve to manage the amount of water coming through the airline, you should be able to reduce it so the water from the tank is just dripping slowly into the bucket. You may find you need a couple of clothes pegs just to clamp the airline to the inside of the tank and/or to the bucket. After an hour or two once the bucket is full you can gently lift the critter out and place it in the aquarium. The process can be speeded up a bit for crabs but I would try and make it last for a couple of hours for snails.





Helpful tips


Clean up time!


Snails are probably the most important part of your clean-up crew but remember they are very sensitive to changes in water chemistry


Hermit crabs can make amusing additions to the clean-up crew and are good at sifting through detritus but can be opportunistic and can try to catch and eat smaller tank mates or annoy corals

Clean up crew - in a nutshell

After your tank has cycled, readings are at 0 and you have carried out a decent (say 20%) water change you’re ready to start stocking with some CUC

Don’t put all of your CUC stock in at first, just put a proportion in and monitor their progress else they might starve

Different snails do different things so it can be useful to have a few different types

Hermit crabs can and will kill snails if they take a fancy to their shells, you can reduce this problem by always making sure there are plenty of empty shells to choose from

Leave shrimps until your tank has matured a bit, although they are a great contribution to any clean-up crew they are very sensitive to swings in water chemistry and can be annoying to other marine tank inhabitants.


Don’t be surprised if your shrimp sheds its skin shortly after being introduced to the tank, they often do this as a result of changes in the water. The skin can look like a dead shrimp so before you start mourning for it check around the tank, they will often hide for a few days after moulting until their outer shells toughen up a bit.




Think carefully before adding an urchin, they can cause problems. Not only can they bulldoze themselves around the tank they are also obsessive collectors and it it’s not bolted they will grab it and wear it. In the wild they do this for camouflage, in the tank they appear to do it specifically to spite the marine reef keeper….




If you are running a FOWLR there are few CUC critters you can add safely as many of your fish will probably be predators.