I've heard that about Leather's as well. What's your pH and calcium? Your calcium is going to have a tendency to drop as your alkalinity goes up. I somehow doubt that keeping your Alk. high is the long term solution for your hair algae problem. Grazers or a refugium are probably a lot better long term solution.

Don't trust the info you get from your phosphate kit. They are notoriously inaccurate and lack sensitivity. There are basically 2 kinds of phosphate, ortho and meta. The kits only detect ortho and the majority of phosphates will probably be present as meta. Hair algae will not grow unless there is phosphate present, so do some deductive reasoning.

Gary