I had a blue spotted sea hare that went to town on my hair algae then it died a week later. There was still some algae for it to eat. Then in my other tank I got a lawnmower blenny that also devoured the algae but it died a week later as well. Again, there was still more algea for it to eat. Currently I have a tuxedo urchin which is doing a good job but I've only had it a few days. I also added a phosphate reactor so that should help remove some nutrients. It's certainly possible I had some other water quality problem that was causing them to die. Whatever you choose, I hope it works out for you.