Caring for rainbow sharks?

On the tank: Putting a young Rainbow Shark (on its own) in a 2ft tank would be fine for a while, you'll be suprised how quickly they grow. Just be prepared for upgrading within months because they like room to swim and patrol their territory. Also they tend to stay at the bottom so a long/wide tank would be better than a tall tank. My Rainbow Shark is in my 50g tank and because it's a community tank he needs that much space. On their own I don't know what size tank he would need.

On the cycling: You could probably get away with cycling the tank with just the Rainbow Shark, the bio-load would be low so the ammonia and nitrite spike would be low. However I really wouldn't recommend it, even a bit of ammonia stesses fish and the fish might die. If the chemistry aspect is a bit daunting there are simpler methods; like putting a bit of fish food in a few times a week the decaying food will cycle the tank, live Glass Shrimp will cycle the tank as will snails. Whatever method you chose a tank should cycle in 4 weeks. A test kit is very helpful but IMO not essential.

In my opinion and experience, you really cannot or should not cycle a tank with a shrimp or a snail. Glass shrimp are actually a marine shrimp and ghost shrimp are a freshwater shrimp. They are small and do not make much waste at all. Snails would be the same and are more 'fragile' as far as water quality is concerned. There are a lot of good methods to cycle a tank without putting any living creature in jeopardy which you can read about here:
http://www.aquariacentral.com/forums/showthread.php?t=84598

There is no way to put a time line on a cycle and so do not fall into a 4 week deadline for your tank. There are so many variables within the process so the best and truly ONLY way to know when your tank is cycled is by using a test kit to monitor ammonia, nitrite, and nitrate levels. When ammonia and nitrite are at 0, and nitrates are present in the tank, it is cycled. You can only remove nitrates by using some nitrate removing filters or by water changes, which is the fastest and cheapest method. While ammonia and nitrites are toxic in relatively low levels to your fish, nitrates, while still toxic can be present in higher quantities in your tank and so a weekly water change is USUALLY the case. Things like overstocking a tank or over feeding are going to raise nitrates quickly and so in those cases you may need to do more frequent water changes or fix the problem.

Rainbow sharks, in my experience, are labeled semi-aggressive, but this is really only because they do not get along with other rainbow sharks and/or other fish that look similar to them such as the red tailed black shark. You are right, they are not sharks at all so you can mix some community fish in the tank with them. While they are not really considered 'bottom feeders' they do spend most of their time in the lower portions of the tank. For this reason, it is important to not overstock the bottom area of your tank with lots and lots of bottom feeders, or the rainbow shark may feel the need to defend some territory. Otherwise, they will get along with most anything. I have a larger one in a 55 gallon cichlid tank. I also do not agree that they grow super fast and would believe that you can keep one in a 20 gallon tank for quite some time. I have had mine since January of this year and it is only 7 or 8 inches long and able to turn around in any 20 gallon tank. This is all especially true if you are going to keep it in a tank by itself.

TropicalNorth,
While I understand that you have good intentions, I do not think that your advice to cuticom is very complete or really very accurate. You may need to spend some more time reading about how to cycle a tank and just how important water test kits are to the hobby. It is also not advisable in the least, from my experience and in my opinion, to cycle any tank with an invert of any kind since they are sensitive to water quality and snails can be burned much more than a fish by ammonia. Ghost shrimp are not the longest lived creatures in the world either, but this doesnt mean that they are disposable and should be put into a tank which will not have a healthy environment. They never stop and eat constantly so putting them in a cycling tank would be hard because they would need a lot of food, and in which case, one could just cycle the tank using fish flakes anyways.

Sure, here he is:


It is fuzzy because I had to chase him out of his little hiding spot and he wasnt happy. As a reference, the yellow lab in front of his is about three and a half inches long

I see what you mean though, I searched for some profiles and almost every site has a different total length listed for it. I always thought they got to about 8 to 10 inches. They are certainly sweet fish though and mine is quite the character. He was the smallest one in a tank at the LFS and got beat up on quite a bit. We brought him home and it seemed like he wouldnt get any bigger and then all of a sudden he had a growth spurt.

Now you got me playing with my camera again! Here are a couple more pictures, maybe a bit clearer.


^That is my largest yellow lab, a male around 4 inches long

LOL, an Oscar would need a 75 gallon tank or 280 liters, I think (I am another dumb American who knows just about nothing as far as metric liquid measurements)

I certainly think that you could, and should put some other fish in the tank so long as you do not go over board and consider all the usual bioload type things. They are sort of reclusive at times and to get those pictures, I had to flush it out with a net from his little home in a tree trunk decoration. Mine really loves eating blood worms, but I cant feed them to him a lot because the yellow labs would suffer from too much of them in their diet.

I really love the rainbow shark. Like I said, mine was very small and no where near as black as it is now when I first got it so dont feel like a gray one cant pick up more color and brightness. You just have to make sure to feed it well and take good care of it. Mine was like the 'runt' of the litter and apparently he is bigger now that most sites say he should get to be.