Angelfish is sick

Question
Hi Ron,

I'm having a very hard time incorporating new Angelfish into my tank. I have a 29 gal glass tank, a Aqua-tech power filter (I'm sorry, I bought it as a kit, I don't know exactly what kind of filter it is). During the first day or two my angelfish (and not always just angelfish, all of them do it) end up at the top corner of the tank. They just float there. Most of them don't move, and they won't eat. Eventually it's like they get swim bladder infection, they start drifting on their sides, then eventually swimming upside down, and die. My water is a little hard, gH registers at about 120 ppm. pH is 6.5 (unchanged), Nitrite level is 0, and nitrate is about 20 ppm. I bought 4 angelfish one day, 3 of them died within the first week. One has flourished over the last month, he's healthy as a horse. I bought 3 more, and within 3 or 4 days they all exhibited the same symptoms, and were dead. I bought a new, larger long-finned Angel yesterday.. I got up this morning and he's in the corner. He ate a little when I fed the fish this morning, and ventured from his corner a little bit, but now he's in the corner again, and I can't get him to come out. I feed the fish a general tropical color-enhancing flake. I hope you can tell me how to fix this, I don't want this Angel to die.. I've gone through a lot of fish these last few weeks.

If it matters any, my two angels are in the 29 gal tank with a red wag platy, 3 small swordtails, 2 serpae tetras (which don't both anyone in the least), 2 danios, and 2 bronze corys.

I hope you can get back to me rather quickly.. in a day or two this Angel might be dead.

Thanks so much,

Cassie

Answer
Hi Cassie,
 It sounds to me like your one angel is attacking and killing the others. When fish are up in the corner that is almost always because another fish is relentlessly chasing them and they are trying to hide.

The best solution is to add a lot more structure to the tank so that no one fish can monopolize it.  When I mean a lot, I do not mean one plant or one little piece of wood.  I judge a tank as having a lot of structure when I cannot see the back of the tank from the front.   That gives weaker fish many, many places to hide and get out of the line of sight of a more dominant, aggressive fish.

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>