Setting up my 150 gallon tank....question re: water changes

[newreefer_59]

My reserve tank is ~ 23 gallons which represents about 15% of my tank. If I were to use the 23 gallons of RO-DI water for my changes, would this require a weekly water change for optimum conditions or less frequest ok - say every 2 weeks? It is a sump setup with protein skimmer.

Thanks.