That depends on the species, how healthy the anemones are to begin with, if that is the only thing that is out of whack in the tank, etc. My nitrates briefly went up to 60 or higher and then I recognized it and began to take steps to bring it down, fortunately it has returned to undetectable and is stable. Deep sand bed in my tank had not been stirred or siphoned, not even the top inch or so, in years. I think that was the biggest problem. So, I siphoned the top inch or so (it's 6 inches deep or so) and did 30% water changes weekly, cleaned the protein skimmer pump so it would be more efficient and over about a month the nitrates dropped down to "zero." Deep sand beds are great for nitrate reduction, but I've learned from experience, they do need to be stirred. Through all this, my anemones were fine.
