Please Help!!!

I have a 75 gallon aqaurium with 3 Orandas and 2 Ryunkins and a black moor.
Alge seemed to be a problem. But I did a 50% water change last week and get
the algea off ever day! My water levels have been tested and they are all
fine. 1 Ryunkin is floating at the top most of the day it has no problems
swimming when I approach the tank it can swim normal and to the bottom. I
changed its food to flake and it seemed better for a day or two. But now its
back to floating again. now today I have noticed 1 of the Orandas is staying
at the top! Im going to go buy som peas to see if that helps. Help what
should I do? I dont have another tank for emergencies! Can I try the epson
salt in the whole tank? I dont want the whole tank to crash! Please Help!!!