A test kit for meta phosphate (the other kind) is just not practical on a hobbyist level. As I recall it takes about an hour just to prepare the sample and involves boiling acid. Any volunteers?

OK there is another method. If anyone wants to lay out about $100,000 for an Inductively Coupled Plasma Spectrophotmeter let me know. I'll let you keep it at my house... as soon as Pete adds on a room for it.