Sorry I should've included more info. The tank is a 40g tall. It has a penguin 200 hob filter and 2 diy filters that my husband made with my airstones in plastic bottles w/ sponges and bio balls. The pH is 7.5 am, n2, & n3 are all at 0. 30% weekly water changes w/ gravel vac. Tank mates are 4 sterbai Corrie's, 5 blk skirt tetras, 2 serpae tetras, 1 Columbian tetra & 2 electric blue rams. The Cory in the pic is the only one showing symptoms and hes acting normal, just has this light brown fuzzy looking stuff on him :-\ Could it be because we made my airstones into fliters and now there's less movement at the bottom? That's the only change we've made recently and its been about a week but I didn't notice the fungus looking stuff till today.