Algae tabs aren't going to cause an algae bloom, and don't use chemicals to remove algae, is a simple fix once you figure out what's causing it, to much light (on to long /to strong) to much bio load abd not enough filtration, do you have an algae Eater like a Pleco or otos or snails, is the tank planted? It's a lot easier to help if you give us a run down of the tank