fish in a barrel
I hope that somebody can answer a couple of questions for me. I have an old wine barrel which was cut in half. It holds approximately 30 gallons of water, some water hyacinth (some stowaway snails), 6 baby koi that were being sold at the local pet store as feeder fish (six for $1) and one anonymous feeder fish. The two largest koi are about 2.5" long and the rest are about 1" - 1.5" in length. I have a solar pump that runs during the day unless we have fog. I am guessing that the water is oxygenated well enough because we have had consecutive days of fog and the fish seem to be fine and getting bigger.
The water is still clear, but I can see some velvety green growth on the sides of the barrel, as well as some little bits of uneaten food on the bottom. Do I need to clean this? If so, is it safe to change out all of the water at once? I feel like I should scrub and rinse out the barrel. Also, I have a second barrel and I imagine at some point there will be too many fish for one. At what point do I thin the herd?
Any other pointers are welcome because I don't know what I am doing. I only got the fish because I have a large potted plant on top of a block in the water and I didn't want mosquitoes. I have gotten very attached to these fish and I don't want to harm them.
Thanks in advance for your help.