I have comet goldfish in a 16 ft round, above ground swimming pool. I have kept them here for 4 yrs. They have grown from 1" to about 8-10" and reproduced. I have lost only 1 to date. By selling or giving them away I have kept the population under control. The water is often like pea soup as I have had no filtration or aeration of any sort. Recently I obtained a small, used floating fountain. I set a galvanized tub on an upturned barrel, filled it with gravel from the driveway, poked some holes in the bottom, stuck in a few taro plants and then shoved the fountain in. The top of the tub is about 1" above water level of the pool. The fountain sprays the water from the tub back into the pool. This has made a small but noticeable difference to the water quality. By trading excess fish for credit at a local pet shop I finally had enough credit to by a 1200 gpm pump yesterday. I plan to use it to build a 55 gal drum bio filter. Found this forum while searching for advice on how to construct,the filter and what materials to put in it. Looks like I can get some help with that here. Any advice welcome.