Bioballs will make a great BB surface to colonize but after the tank runs for a while they will begin trapping lots of debris which leads to high nitrAtes a lot of time meaning frequent cleanings of your bio balls. Because of that people choose rock instead since the insides harbor anaerobic bacteria which is one of the last stages in the nitrogen cycle. The deep sand bed will also create a safe haven for that bacteria but you'll need atleast 5-6" of sand. I would just do what was already stated and replace them with a bunch of rock and macro algae. As for the deep sand bed if you want one I would run it in your DT where it will be more effective.
