Please please help-Angelfish sick-unclear what medications?

I hope this is in the appropriate area-didn't know .
I have a 60 gallon tall angelfish tank with five angelfish-1 is the size of a softball and the other 4 are the size of 50 cent pieces. Also it has 4 little Corys and 3 bristle nose plecos about 1 inch long each. My water perimeters are nitrAtes-10, nitrItes-0, ammonia-0, ph-constant 8.0, KH-180 and GH-between 150-300. I do a 50% W/C once a week. It is a highly planted tank. The filter is an emperor 400 for up to 100 gallons.
A couple of weeks ago one of the small ones started to have a some flaring of its gills and breathing rapidly and just sitting on the bottom in a corner. I treated the tank with API Melafix for seven days and it seems a little better-but still breathes rapidly with flared gills-but does eat fine and is active. Now I have 2 others of the small ones doing the same thing-breathing rapidly, not eating and sitting on the bottom in a corner even though I treated the tank-I thought maybe a bacterial infection. No signs of any external parasites that I can see. The Corys and plecos are fine. I don't know what to do-I want to treat with the right medication rather than over medicate -trying this, that and the other thing!! Is it flukes-angelfish virus-bacterial??? I don't want to lose my little guys!
Any help would be greatly appreciated,
Thanks-
Retha

 

Can you attach a pic?

Do you have a separate QT tank?

 

The picture isn't the best they were all skid dish of the camera.

Unfortunately no-I only have a 75 gallon tropical community tank besides this one.



Another picture



Another picture

 

I wonder if the bigger angel is stressing the little ones out or bullying them, since it's only the little ones affected.

 

No the big one is very docile-he was a donation fish that was in a ten gallon tank completely by himself and hardly had room to swim-I think he enjoys their company-at first a couple of the little ones were picking on him-but now, even at feeding time they all get along very well-no bullying. Hopefully it will stay that way.

 

While you may not see overt bullying when you look at the tank, it doesn't mean it isn't occurring. Just because he lived in a tiny tank alone doesn't mean he can't be a bully. Just throwing that out as a possible cause. They are cichlids, after all, and there is a size difference between them.

 

So if that was to be the case-and put the sick little ones somewhere else to relieve stress-I still don't know how to medicate -or once they were not stressed would they just get better naturally?

 

They might!

 

I would get a storage tote from Walmart or target and set that up as a basic hospital tank. Then I would take the big one out and then watch the little guys closely and see if their condition improves. If they don't look better within a day or two then I would take them all and put them in the tote and treat with broad spectrum antibiotics. (do this in the quarantine tote so you don't trash your bio-filter in the main tank.
It's probably just stress from the big fish, so until you know for sure I wouldn't stress to much.