I don't think very many people will advocate the use of chemical algae reducers in your tank. The algae is not harmful to the turtles and killing it with chemicals adds to the waste load in your tank. I hate the algae, too, so I understand why you want to get rid of it. Try turning your lights off for a couple of hours in the afternoon. A pleco or a snail would also be helpful, even guppies will eat the algae. If it is on the rocks and "furniture" in the tank just take them out and scrub it off. I would try a lot of things before using the chemicals.