Hello all, I have lost 3 rams in 3 weeks. My tank: About 15 gallons, moderately planted, temperature 26C/79F, pH 7.4. Tank is 7 months old. Ammonia -0 Nitrites- 0 Nitrates- 40ppm (50ppm from tap, I bought some seachem denitrate and matrix that are supposed to reduce it plus nitrate consuming plants - hygro and water lettuce.) The following fish have been in the tank since the beginning: 3 albino cories, 9 cardinal tetras, 1 honey gourami I have bought a pair of rams from the lfs. Slowly acclimated. First one died within 4 days. Heavy breathing and not eating. Took it back and the lfs checked my water and gave me a replacement. This time I got 1 more female in case there was an aggression issue I hadn’t noticed. New fish seemed very healthy. The original male formed a pair with the new female and even spawned. Then things started going downhill. The male started flashing (no white spots or anything). Then all the rams started doing it and then the gourami too. The male had inflamed gills. I started treating with paraguard which is mild. Other fish stopped flashing. Male kept flashing and gill plates wide open. Still eating and active but heavy breathing. After a few days of paraguard the male started getting worse. Very inflamed gills wide open. I thought that it could be gill flukes. So I bought praziquantel. But it was too late. The male would hide for 2 days until eventually it died. When it died I checked its gills to check for worms. I couldn’t see anything but the gills were white! I then started treating with praziquantel and the second female ram started losing colour, flashing a bit and heavy breathing. Yesterday she lost all her colour. No inflamed gills or anything but heavy breathing and her belly was a bit swollen (full with liquid?) even though I hadn’t fed them. Eventually she died last night. As soon as she died I checked again for flukes. Nothing visible but white gills. The gills were also very tiny, as if they have rotten away. The last female is looking very good. Breeding colours, very active. What’s killing my fish? What should I do?