When I was breeding apistos, I used 10 gallon tanks with Hydro-Sponges and about 1/2" fine sand with some live plants and a 2" clay flower pot lying on its side. This worked well with the smaller breeders but when I started breeding the altispinosas and others a bit larger, I had to switch to using 20's. With my full grown breeder bitaeniatas, N. anomalas, macmasteri and cacatuoides, eunotus, I switched them to a 20 gallon. The problem with my bitaeniatas and eunotus they quit spawning after I put them in the 20's so I had to put them back in the 10's and they began spawning again. I also quit using dithers. I found my apistos spawned better just by being able to see the breeders in the tank next to them. At one point I had a spawn of cacatuoides growing out in a 55 gallon tank with nothing but a Hydro-Sponge and I found they had been spawning in the 55 after I went to catch some to sell! It is possible to spawn them in the 10's. I myself wouldn't go less than a 10 gallon. Other breeders might. Just one breeders experiences. Kaycy