I'm in the final stages of acquiring equipment for my new tank build and the last two things to buy are the RODI and saltwater mixing containers. The plan is to build them very similar tho the water change station in Walter White's "200 gal forever and a day" build thread... two large containers with an external pump plumbed together, and to the sump, controlled by ball valves... anyway... Is there a rule of thumb on how much saltwater and RODI water to keep on hand? In the past, I have always had 40 gallons ready(limited by the size of my Brute trash can). My thought for this build is that I would have 50% of my total system volume ready in the saltwater container and the same amount again in the RODI container. That way, in the case that I needed to do an emergency water change, I could do 50% right away and have enough RODI to quickly mix up for another 50% water change. My only hangup in my thought process is this would require two 175 gallon containers, which seems excessive! What do you guys think?