If he has alot of HA then the test will come back as 0 as the HA is eating it up. Algea lives off P04 as well as co2 and a miread of outher particals in the water to much light is what set my algea in to action. everything was great untill a timer for my lights didn't work to right it would come on and not go off when it was set for. Afew hours latter it would turn off for no reason at all. I checked the programing on the timer and it was right. changed to mechanical timers they always work and they never loss there programing. I borowed a larged sea hare and he cleaned up pritty much everything except a couple of spots he would venture over to them but would not eat from them I found out that if there is any of the hard type of macro algea they may not eat that area. I not have a sea urchin and he eats it also my angles eat it. things are good now.

Bill