I have a 160 gallon stock tank outside which holds 5 feeder goldfish. They are getting larger every month. I bought them about 6 months ago, and they have grown about 4 more inches in length, and at least an inch in width. As with all of my tanks, I have no filters, just air lines with bubblers or airstones. Plants do the filtering. I have water lettuce and duckweed floating on top of the water. When I first put the fish in the tank with they were very small (17 cents ea. feeder goldfish), and I never saw them eating the duckweed. But as they have grown, I see them munch on the duckweed upon occasion.
So far, I am able to keep at least half of the surface covered in duckweed and some small water lettuce (no direct sunlight on tank so plants don’t grow very large). The duckweed supplements the cheap pellet food I give them. Their colors are vibrant and the fish are growing very well with the cheap pellet food and duckweed. But I would like to give them table scraps too. I often have leftover rice and vegetables that are cooked and plain (no oils, etc.). So I found a list of foods that will help supplement their diet of duckweed and pellets. I have listed these in my ‘Goldfish Feeding’ page for reference.
I have added 4 heaters to the stock tank, because I had some extras laying around. They are a mix of older heaters, from 20-75 gallon sized heaters. I am hoping these will keep the floating plants from freezing in winter. I had two old water hoses, and wrapped the tank with them. The pictures show the two hoses wrapping the tank for insulation, but I have since added three more that were donated by friends because they were full of holes, and have the tank wrapped almost to the top. The bottom hose is attached to the tank, and I can unwrap it to drain the tank if need be. I have done nothing but add water to top it off from evaporation. There is a ‘pop-up’ plastic greenhouse surrounding the tank, so that will help as well. It has lasted two years so far, with a few holes popping up here or there, which I cover with clear ‘Monster’ tape from Lowes Hardware store. The bottom of the greenhouse shows the most wear from weather. I’ve placed foam board inside around the bottom of the greenhouse. Maybe it will last another year? I hope so. Otherwise, it was only 125.00 dollars, and for two years of service, that is not too bad. I think it looks nice too.