Angelfish behaving abnormally

[Eelzor]

My 4 angelfish have been doing this strange behaviour for a few days now. I believe it was breeding season for them about a week ago and they were in pairs and occasionally fought each other. Only recently they have all been in a close group, staying close together in the corner of the tank, near the surface. This has been going on for a few days and it starting to concern me. They move around the tank only sometimes. My water parameters and tankmates are not a problem as they have been living in the same water and tankmates for a year or more now with no problems whatsoever.

So these are the strange angelfish symptoms,

1. All close together
2. Not moving much
3. In the corner of the tank
4. Near the surface of the water

BTW, just a note that they are still eating.

Cheers, B)

Edit: I just remembered that I had also recently put large rocks in the tank. These were thoughroughly cleaned though. No other fish if affected though and several of the other fish in my tank are supposedly more sensitive, so I don't see how that could be a problem.

 

[Tempestuousfury]

Are you sure that the rocks don't affect pH?

It might be O2 deprivation, what with the lethargy and staying near the surface. Is their gill movement abnormal as well? Try a few airstones or even a bubble bar to disturb the surface and add to the circulation.

Tank temp?

 

[Eelzor]

I took the rocks out and the undersides of them seems to smell a bit rotten. I think that was because air was trapped under them, creating dead spots. Before I add the rocks I will add an airstone first and see how it goes from there. I still think that not enough oxygen was the reason they are acting like this. My tank temperature is 26C, or 79F. The 50 Gallon tank is in my sig.

I'll account what happens, thanks for help as of yet.

 

[Eelzor]

Success, simple common sense praviled and the air stone is bubbling to the maximum and the angels are more active. They are still a little inactive but I guess it just takes time for now. The main thing it that it's improved and the problem is found. I might consider putting those rocks back in now. Would you think it's safe? The rocks were simply called "Riverstones" and I got them from a nursery. I wouldn't know exactly what there made of but help on that subject please.