I broke down a tank about 3 months ago, and began to put it back up last week after a little restoration effort, resealed it, put a new frame on it and got all new accessories filters, heaters, light glass canopy etc.... I filled the tank about 30% to test the seals/frame placement, didn't want to fill it up all the way right away fear of flooding. I went to check on the tank 3 days later(yesterday,) and there was fungus on the bottom of the tank. any ideas why ? best way to clean it out ?