I think a lot of us learned that having 1ppm,2ppm or even 3ppm of PO4 is not as "deadly" as per previous myth.
I wouldn't state the question the way you did. Having 1.5-2ppm is not "universal" formula and has to be tweaked depending on your fishload, fish feeding and NO3 consumption. If your NO3 is creeping up, add more PO4 to help "digest" NO3.
Sorry, that's just my inexperience showing Sadly I can't edit it, so change it to do you dose PO4. I think I will give this a try, having som very minor problems with green algea on the leaves of a couple of species.
I use Fleet Enema to maintain PO4 levels around 0.5-1ppm, you can easily double that amount IF every other element is also well balanced. High PO4 levels can create problems if other imbalances or deficiencies are present.
In absence of a PO4 test kit, I usually find that if I need to dose NO3 to maintain it above 0ppm, I will also need to dose PO4.
My discus show signs of breathing problems when I brought po4 up to 4+ ppm. This was by accident of course. It was a quick reaction too; within 10 min, they were gasping for air. I did a quick water change and everything was back to normal.
I use KH2PO4 in my tanks. I keep the levels at about 2 ppm. Ever since I started keeping PO4 at this high level, my algae problems have actually been receding. My Anubias barteri v nana leaves are clean as a whistle and are inches away from 4 wpg of lighting.
Woha, that's a bit of a surprise for me After reading the papers from Colin & Sears, PO4 has been the enemy in my tank. If I could only get my hands ond some KH2PO4 quick.... Guess I should try to order some from the PMDD store, and check this out for myself. Have been having slight problem with green spot alge for the first time in two years. Guess it was to good to last Thanks for all your input!