I have a small pond and plenty of room for babies. Depot, my four-year-old goldie, lays eggs in her tank all the time so I don't forsee any trouble breeding in a tank so long as I move the eggs to a different tank, Depot likes to eat them. I'm hoping to get some real good colours from her babies. We move them into the pond in summer and in tanks in winter. Recently my sister go a new fish and didn't quarentine so it killed off some of my mom's older fish. All she has left is a female comet mix of sorts so there is empty room. So far the new fish seem healthy but they will be in the quarentine tank for a month at least so no babies until then.