I bought 15-20 fry and grew them out. As they hit the 6-9 inch range I started selling off. I think 1-2 males to your 6-8 females sounds good. Make sure you have a really good filtration set up as well. I know a 220 is a big tank but when they get really big you will be happy you stuck with the 8-10 range or a few less and heavy filtration, at least that's what I've gathered from my experience.