...bala sharks get HUGE!!! What kind of pleco do you have?, if it's a common pleco your looking at about18 inches, the bala sharks, red tailed sharks, irredecent sharks are incompatable, the pleco will not harm your fish but I suggest getting a MUCH bigger tank!!!! Plecos do need driftwood as a sourse of fiber.
I suggest you start over with something a little easier like mollies and platies.
hope this helps!
-bobo