Thanks for the tips. I'm looking forward to some of my own observations as well in correlation to ORP level.Remember that ORP isn't a 100% verified measure of water purity. Some aquarists use it that way and others don't even monitor ORP. I monitor it because I use ozone and an ORP controller is the safest way to do so. However, I've personally noticed that ORP levels are indicative to how my corals appear. Usually when my ORP is up above 300-350 mv - the corals appear great and are extended and beautiful. If it drops down closer to 250 some are closed up, etc. That is entirely anecdotal and could be totally unrelated, but it's a personal observation I've made over the years. When I worked in public aquaria ozone was commonly used on a wide scale, both to maintain water quality in large displays and to sterilize water during a mass filtration-cleaning period. In this case, ORP was run up to 600+ mv then given time to off-gas before being used. The goal was to kill any potential parasites within the water.