I really don't think you have adequate lighting to keep anemone's or light demanding corals. As I understand, you have 150 watts of light over a 75 gal. I hate to use the watt per gallon rule, but usually it is recommended that you have over 3 watts per gallon. You only have 2 watts per gallon, not nearly enough for an anemone. I wouldn't worry about the nitrates, just don't let them get any higher. Have you tried to feed the anemone since you bought it? I would have to disagree with your LFS, I have 3 BTA's and they have never looked like that.