sick yellow tang?

Question

I have a 36" marine tank, it is about 6 weeks old. I have a yellow tang, 2 tomato clowns, a long nosed hawk, a cow fish, a cleaner shrimp, a decorater crab and a red leg hermit crab. I also have 2 soft corals. I use a skimmer, a hagen external pump, 2 powerheads and T5 lighting 99 watt white and 21 watt blue. the water tests as near perfect every time using 3 or 4 different testing kits. Anyway, my yellow tang is acting very strange. It has stopped swimming and lays on the bottom of the tank, if you touch it with the net, it wakes up and tries to swim, but soon sinks. It looks ok, no colour change, no spots or anything that looks suspicious. can anyone suggest anything please. p.s. I don't have a quaranteen tank yet. BTW, the last fish I put in was the cowfish. and all the rest of the fish are great.

Answer 1

There are too many fish for a tank of that size (I'm thinking it's a 30 gallon because of the length, is that correct?). A yellow tang can get to 12", the tomato clowns will be between 4-6" (the female will be larger than the male), and if your cow is a longhorn (named for two projections over the eyes), expect up to 18" there. Cowfish can also give off a toxin which can harm (or kill) other fish in your tank.

At six weeks, your tank probably hasn't cycled completely, so my guess is that your tang's being affected by ammonia in your tank. Ammonia is toxic to fish, and your tang may just be a little more sensitive than the others - they should only be introduced after the tank has been running for about 6 months. If you have a saltwater aquarium test kit, I'd recommend a fast check of your water chemistry. If you don't have one, I'd suggest a 20% water change, and getting a kit in the near future. If ammonia is the problem and no water change is done, soon all your fish will be affected, and you don't want the cowfish to be stressed - it will release the toxin and you'll have more than an ammonia problem to deal with!

You should also check your pH, salinity, and water temperature as well, if the ammonia isn't the problem.

I'd also suggest returning the tang and the cowfish, and not introducing more fish until your tank cycles.

I'm adding a link below which give more information on cycling a tank.