Here is an enlightening article on phosphate and its effect on saltwater aqauariums. 1ppm won't kill but it certainly inhibits growth.
Phosphate and the Reef Aquarium by Randy Holmes-Farley - Reefkeeping.com
I offered the sea hare as a potential solution as I have used them in the past. I have yet to have one starve as I take them back to the beach once they have finished their job or to a pet shop for credit. I believe Tony is on the right track
as evidenced by his photos. Nutrient control and good maintenance will reward the caretaker with healthy and happy stock.