tony

I had 4 or 5 cherry barbs in my 20 gal. tank (see below). All of the other fish are doing great, but the cherry barbs just keep dying. Now I am down to one. They stopped dying off a few weeks ago, so I think that the one that I have left will be fine. I would just like to know if anyone can give me a reason for the cherry barb deaths. Thank you

P.S. This is not the first time that this has happened with the cherry barbs.

sirdarksol

What are the ammonia, nitrite, and nitrate levels in the tank?
My first guess would be water quality, though I'm kind of surprised the otos aren't going first. That tank is overstocked, and the water is probably pretty high in nitrates, if not ammonia and nitrites.

The other possibility is the shark. How large is it? Rainbow sharks are very territorial, and it may be taking out what it sees as threats. Once done with the barbs, it may move on to the tetras, and eventually the cories and otos. Especially because it's with so many other fish, it may just be feeling very defensive about its space.

tony

The water quality is good. The last test showed the nitrites at 0, ammonia 0, and the nitrates 20. I stay on top of the water quality as much as I can. I do a 25% water change every week, and have it tested in between water changes. I have a penguin 200 and a penguin 150 on the tank. As for the shark, it could have been him, but I seriously doubt it. He is very small (about the size of the cherry barbs) and I have NEVER seen him act territorial towards any of the fish. He is very shy, and stays in his cave for most of the day. I just can't figure out why only the cherry barbs are dying.

P.S. As for you wondering why the ottos had not died before the cherry barbs, it is because the ottos were added to the tank after the cherry barbs had died off.
Thank you