Long story short made a rookie mistake and forgot to clean my filter during regular maintenance and shot disgusting water into the 30 gallon tank. Cleaned it again after and added an extra sponge filter just to be safe but the next day my flowerhorn had a strange gash behind it’s gills. Assuming it’s some sort of parasite like HITH any help would be great. Did a 50% water change when I saw it on Monday but no improvement... guy at the lfs said it didn’t look like anything but he must not be seeing what I am.