Anemones need pristine water that is stable which is why they are recommended for established and mature tanks. Having nitrates and phosphates is a likely culprit for your unhappy nem. You need to determine what is causing those levels (most likely overfeeding) and eliminate the introduction of those before you can reliably remove them from the water via weather changes. Not saying don't do a water change but you must understand that reducing the level by a water change will only temporarily deal with the issue until the reason for the nitrate and phosphate is addressed. Like I stated above its most likely over feeding as that is the primary source of phosphates. Something else to note, if you feed frozen foods you should rinse it with rodi
water before feeding. This will help reduce the phosphates being introduced.