I recently adopted my brother's guppy tank, because he needed help getting levels under control now with levels almost good to my knowledge(doing the testing tomorrow) But I just realized that one of their gill areas is puffed out, with "stringy cotton" like strands coming from a "cotton ball" looking thing in his gill. It is almost white, maybe a little grey. parameters will be up tomorrow some point in mid to late afternoon. The tank is a 15 gallon I believe, 2 guppies( I know they are schooling there were more but we wanted to get everything under control before adding), w/thin layer of gravel substrate Thanks for all help!!