I am not even sure what clean water means for these corals. I think they are a lot more tolerant of high nitrates and phosphates, or at least phosphates... which we know is harmful to SPS... but they are prone to shut down when the water gets too murky for long periods of time, whether from food or bacteria. This applies to Dendronephthya as well. The gorgs are sensitive to large water changes, which presents a challenge since they require several feedings per day. Just my limited experience so far.