Fancy Goldfish like to play
I have 11 (R.I.P. Flip) fancy goldfish that 'appeared' in my 250l wildlife pond after I bought some Elodea for the frogs to eat... The pond had a solar air stone, some oxygenating plants, 3 frogs, 400 snails(...) and no filtration or water changes. I filled the pond from the hose pipe - no de-chlorination, didn't provide food, no water changes and since it was summer the water was hot. Essentially I did everything wrong and 11 little fishes spawned and thrived for their first few months. Poor flip spawned in a bucket as I had cut some of the elodea back and succumbed to bloat problems.
With the pond being too shallow to survive winter and too small for mature fancies I brought them into a 100l indoor tank. I know WAY too small for 2 fancies, nevermind 11. They're around 3 months old now and I'm splitting the group up into 2 tanks, then later a third. Once they're full grown I'll let some of them go, for now I want to see what they grow into (looks like Ryukin and mixture of fantail and butterfly).
I keep a spray bar above the water line. The goldfish play in the stream, but sleep away from it. The agitation helps the air content in the water as well as moving the waste to the outtake hose which, given 11 messy goldfish, is essential. The bar runs back to front not side to side so the fish have plenty of quiet water to rest, plus the ornaments and plants provide a barrier and hiding.
My current tank contains elodea and a java fern, but gravel substrate with algae cover decor. Next two tanks will be full planted - the goldfish are welcome to eat the plants, they'll never get through them all (probably...)
From zero interest in fish to slightly obsessed in 3 months...