Once again, I have a 90 gallon Fish/Live rock tank. I recently had a minor bout with Ick with my Powder Blue Tang (everything has been good for 2 weeks now). The more I read the more scared I get. Therefor, I am looking at more thing to make her environment better. So, I was wondering if anyone uses Trace Eliments. If so, how often? Is it a must, a luxury, or a waste of money? I do bi-weekly water changes (about 15% each time), is this enough to not worry about the lost of eliments, or shouls I step that up?