Fish at the top of the tank

[mjime714]

A friend of mine was having the same problem and it turned out there was a lot of chlorine in the water from his tap. I doubt that you have the same problem because there were fine for months, but I do believe it has to do with the chemistry of the water.

How is their appetite and behavior?

 

[Tango374]

They eat great. The new fish I introduced is a 3'' peacock and was taking food 20 minutes after being put in the tank. 3 days later is when I ran into this problem. Right now in the tank I have:
one 6'' male ahli
two 4'' female ahli
one 1'' ahli
two 3'' moorii
one 3'' male peacock
I am starting to think it is a stress issue. the only fish that stays low in the tank is the aggresser...the male ahli.
any thoughts?

 

[mjime714]

maybe they are all scared of the Ahli. He must have gotten all agressive all of a sudden
.

 

[guppy]

Is the new fish picking on them?

If they are not gasping at the surface, then it sounds like less of an oxygen problem, more of a stress issue.

Since they are not gasping (low O2), or laying over (intestinal infection) and your parameters are currently good I think Miles is right, you probably have a tank bully. One thing that helps with this is to use structure (rocks or wood) or plants to break the tank into a couple smaller, distinct territories. The bully will tend to hold an area and return to it quickly instead to constantly harrassing the others. At least it works with cockatoo apistos.