Is it gill flukes

[Porto Covo]

I have lost two discus to what I think is Gill flukes. Classic signs of a protruding gill, heavy breathing and not eating. I have done several water changes. I live in Portugal so medication is not the best. I have used Wormer plus, no effect. Added salt still no effect. I then tried fluke solve no effect. I have just tried Bilocil which seems to have done the trick. I say that as there is one still alive and effected which is moving around the tank a lot more and is not staying in the corner but still has a gill which protrudes. However, as I see the fish moving around the tank more they are not eating and the side effect is that it has killed my Rummy nose tetras. Despite the claim that it only effects catfish etc. So can anybody tell me more about Bilocil? will the protruding gill close up or could this be something else?. The tank is an establish 600l tank which had originally 8 discus but now 6 discus. Filtration is by way of a canister filter. I do a 25% and a 50% water change per week. All parameters are good. I use tap water through a set declination filters. The fish are 3 years old. Any advice welcomed.