I just finished changing the water and gave the last dozen or so Tilapia to my neighbor a few minutes ago and he said they were going to have a fish fry for dinner. I'm filling it back up and am going to try and get the water clean enough to raise goldfish. Right now there is about a 1/8 inch layer of brown goo all over everything. 'm trying to decide between waiting to see if it greens up on it's own or putting in a handful of fertilizer and waiting a few weeks.