You can't bring them down safely. Your tank will decide where it wants to sit. It takes time. Redox levels don't swing that much from 250 - 400. Mine swings 40 points. In fact a 10% water change does not affect the ORP that quick. Water changes are good if you don't run ozone. Fauna Marin asked me to do 10% changes a week...at first I was reluctant...but the benefits from it are showing. Your water should be RO/DI not the bottled stuff....Do your readings fluctuate over a 24 hr period? When you clean your probe the reading should be low but they eventually rise? Does your redox reading change if you go from high flow too a low flow area(sump)? If no to those questions then your probe is screwed. I would take your probe and plug it in into another tank to see if it make a difference. Find a tank with good SPS growth.
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