I have noticed today that one of my fish had white stringy, translucent poo. It is eating ok and looks healthy enough. A couple of the other fish have one small white spot on their tail fin and one has a small cotton bud on his dorsal fin. There are 8 discus in a 340 litre tank all appear fairly happy and healthy. The fish are all about 5 or 6 months old about 4.5 inches apart from one who (might be stunted?) is about 3.5 inches. I have had the fish about 6 or 7 weeks. I have been water changing every day about 60% one day and about 20% the next using HMA water that is heated and circulated for 24 hrs before it's pumped into the tank. All parameters are good 0, 0 and 10. Ph is 7.8 as always. I am running two large cannisters with UV built in. The only action I have taken so far is to soak granules in epsom salts for feeding (just started that). I have also ordered Esha Hexameta to be delivered in a couple of days. I have tried to source metro (can't spell full word) but can't find any in the UK. I think it might well be hex but am unsure as I've never seen it before. Any help or suggestions would be much appreciated.....Feeling anxious.