I have added 1500 mg of vitamin C, than a week later did it again. On the DO, I have about 1,200 gals per hr. going back into the FT thought my aerator ring and the same amount doing a splash down into the FT from the GB. The only time they come to the surface is when being feed. Not overstocked, no kids or pets to stress them out, none of the gold fish have it.

PH @ 7.4, Ammonia has always been under 0.25, Nitrite has always been 0, Nitrates was up to 160 but is down to 60 since my large water exchange. This problem started 3 weeks before the water exchange.

If my FT holds 650 gals, GB holds 300 gals, filter holds 55 gals, how much Epsom salt should I add? Or I'm I just treating the sick fish and not the water in the FT. If so can I add the Epsom salt to a smaller tank and just treat the sick ones? How much Epsom salt for a 10 gal tank and how long do I leave them in there?