http://www.aquariumadvice.com/viewtopic.php?t=6419&highlight=musty+smell
Recently my 55 gal has started to smell RANK! It stinks up my whole room. All I have in it is a 14 inch silver aro, 2 plecos, and a craw daddy, craw momma, and some craw babies. Ac ouple weeks ago, sfter being fed up...