For a ten gal. tank, six Neons and three Platties is close to the limit in terms of optimum tank space for it's inhabitants, but you can maintain that number of fish types in that size of tank if you (A) Do water changes at least once weekly (B) Change your Platty ratio to one male and two females (C) have a couple of plants (soft if artificial) for the female Platties to hide in if necessary when they're pregnant.. another thing I'd like to tell you is Neons are a lot more fragile than Platties, so if for any reason you get say an
ICH infection in that tank, you may want to seperate the two species for treatment.