Bala's dont that fast, at least not mine, but they can reach 12". Mine grew from around 1.5" to 4 inches in about 6-7 months, you seem to have plenty of filtration, but want to be sure your Bala's have enough space when fully grown.
We'll unfortunately I don't think I can keep my shark cause someone's attacking him and I'm not sure who it's either the filaments or the pacu ; ( so I'll have to see if I can trade him away at my LFS
