Well, I wouldn't even run a reef tank if I wasn't using RODI water, especially here in Iowa with our awful nitrates. Sure, you could probably do it and things might be fine. Inverts are always more sensitive to water quality, imo, and I'd spend your money on bettering your water quality first, then once you have that under your belt, think about getting a pretty clam. It's not as fun to spend money on things like an RODI unit, but it may save you headaches down the road, such as algae issues from poor water quality or save the lives or prolong the lives of your tank inhabitants.