Ok I got question while were talking about algae, A couple months back My Rodi fiters were brown, Really Bad time to change I use the kent marine Rodi unit, I went to my local fish store to buy replacements it took him over a month to get one of the filters so. I slacked on doing water changes and i was use tap water for top off. I know EWWWWW.. I developed brown crap on the rock work easly wipes off with a brush, I 'm thinking it was caused by bad water where I live ( There Constantlly doing road work out side bad water here) Someone told me it was Called not sure if this is a word (Tridas) Has anyone heard of this? Bascilly I wiped down my rock work and finally got my filters running again did some water change , Im on my second one Looks 100% better... But I still have some of the crap laying around , Are there any critters/fish that like to eat this crap?