I used too have 8 fish and now I’m down to 3 most have randomly started showing symptoms like fast breathing sluggish and just laying there or not moving and I have treated the tank with prazipro in case it was flukes or some parasite but it doesn’t seem to be helping it randomly comes and only infects usually 1 fish at a time the water quality is perfect I have no idea what is going on someone please help there is no photos because nothing is visibly wrong with the fish at all someone please help