My stepdaughter's 30 gallons tank with 4 Glofish. I read that they are supposed to be in a group of 6? We were planning to get more after I got her tank cycled. Ammonia is 0 ppm nitrite is 00 pm and nitrates is 5.0 ppm. They have been aggressive and I believe they got to one fish's fin? Still good time to get more?