I have a friend that tried it and it made a mess of his corals. I got some of them and after about a week they looked just fine. He only had a tomato clown and a sargent major at the time, they weren't effected.
Any idea where the nitrates are coming from? Food and water is the 2 biggest ones check the water you have mixed up before doing a water change some times the RO
unit will need new filters. If you are using frozen food thaw it and rinse it if possible. If I can't rinse it I use a paper towel to absorb the water and then add a little RO
water then absorb that too.