Is the size their max size or their current? If it's max, i'd go for 2-3 more blues. Then again, your filtration matters too.
I've got 54 microrasboras in my 30 gallon with 3 otos and cherries. I almost have no need to dose nitrates.
I'm also thinkin of adding a blue ram to make the rasboras school a bit more than they do.