for me personally i would rather keep all boy or all girls on one tank of water,, i have my 2nd 10 gal partioned off but the males can still see,, and smell the female,, and i think it is irritating everybody on both sides,, ,, even with a see threw barrier my boys got used to seeing each other ,, the occasional flare but nothing magior,, now the one that i am not sure is boy or girl swims up and bugs them both... if u have a 7 gallon i would try to devide it in to 3 spaces,, and then have 3 boys,, or go the oppeset and not devide and have a hole tank of girls,, but even the ladies can get nasyt so when keeping girls togather have at least 4 so the aggression is spread out,, 5 would probally work best ,, leaves alittle more than 1 fish per gal space