Your current pace of roughly one percent daily is well within a safe range for a one hundred fifty gallon system. Spreading that volume across three hours with short intervals actually helps more than running it continuously, because it gives the tank time to equilibrate between each addition. I generally recommend keeping daily changes under two percent until you confirm that your calcium, alkalinity, and salinity remain flat over a full week. If you notice any parameter drift after switching to automatic changes, slow the rate down further or extend the runtime so the water enters more gradually. Corals and fish tolerate small, frequent adjustments much better than large weekly swaps, even if the total volume is identical. Monitoring your specific gravity and alkalinity closely during the first ten days will tell you whether the current schedule needs fine tuning.
