Well you need to move onto normal food once you've read the garden peas once. The peas are a laxative so the fish are going to get worse if you feed nothing but peas. Now you've cleared them you need to start feeding them up to strength.
It is done if theres poor water quality, but you could ahve poor water quality if somethings got in which normal tests cant test for
Only treatment you could add if you wanted to was salt and possibily a strong anti internal bacterial treatment.
I have been feeding the fish normal pellets soaked in pond water for a few days now and i'v also done a 50% water change. How long before i start to see any improvements? p.s thanks for everyones help :)