BigJim, YES, I had the exact same problem! I used neutral regulator for a long time and could never figure out why my tank looked like a big, green algae swamp, until I finally heard that it might be phosphate based, which it turns out it was. That, along with blue-green algae colored my first attempt at plantkeeping very unpleasant, indeed.
I hate to be the bearer of bad news, but those phosphate levels aren't coming down anytime soon. In theory, everytime you do a 50% water change, you should reduce the phosphates by 50%, right? Unfortunately, I discovered through endless cycling and head scratching that the gravel was acting as a phosphate battery, replenishing my phosphate levels within a day, everytime I cycled. It would go down a little and then spring right back up to something higher than what the test kit could measure. After several months of cycling my ass off, I finally took down my smaller tanks and rinsed the gravel in each one and set them back up from scratch. With my 75 gallon tank that would take me a week, especially since I have a very deep gravel bed in there, so that wasn't an option. I finally just loaded my canister filter to the brim with PhosBan and PhosGuard from petwarehouse.com. I'm guessing if I took out all the phosphate remover stuff, the levels STILL might go back up, but as it is now, they run at .5 PPM on a regular basis, which is a very comfortable level.
I highly suggest you either take the tank down and rinse the gravel thoroughly or just take the lazy route and pack your filter full of phosphate absorbing media.
Two 1 GA desktops, a 5 gallon, a 2.5 gallon, a 10 gallon, a 20 gallon, a 25 gallon, and two 75 gallon tanks, all planted.
I am an expert on algae, so ask me if you have questions. I know how to grow it, just not how to get rid of it.