run the pumps in the rez just when you flood. Maybe start the air pump 5 minutes early. I don't think 24/7 will deminish the iron but why do you really need it all the time. Those running all the time are running bubblers and DWC where roots hang in water constantly. What's the point in a rez for flood, you only need air when you flood. Other wise it's like beating a dead horse. When the flood table dries out don't the roots get air ? If you could put it in the flood table I would say 24/7 but that doesn't work.