I have a 90 gal tank with two powerheads, I have only been using one, my corals are mostly moderate current types, but I would like to add the second one to change up the flow a little. What is the best way to do this? Someone mentioned timers, but I need to know every how often should they alternate, and should they run simultaneously at any time during the day and for how long. Also, any suggestions on which timer I should look for? Thanks.