rrasco I would just manually run the reservoir and only when it's empty. no reason to have the RO/DI unit come on automatically. when you see it low just start running it and let the auto shut off system /float valve shut it off . it's better to run it 4 hours than on off. I have two 55g linked and when they run dry i go turn on my filter and water grass with waste, then just use the up water till I need to make more water.