Maybe move some of the fish (bala sharks) to your 55 as your 10 is way overstocked. I would try to get that straight before you look at buying anymore just yet.
The balas need to go in the biggest tank you get. Just think that even in the 55 balas will grow to 12 inches. Your tank will only be 48 inches meaning they only have 4 times their body length to swim. That isn't very far at all.