I've recently used three different GFO media, Pora PhosLock from a local LFS, Phosban from BRS and RowaPhos. The Rowa is by far superior, in my opinion. The Pora took a lot of rinsing before the water runs clear, The Phosban warns not to let it tumble too much or it disintegrates and I don't know how much is "too much". The RowaPhos is the most expensive, but considering the investment we all make in the hobby, a few bucks more for GFO is peanuts. When I replace GFO, I make it part of a water change and use tank water to run through the reactor after filling it with new media. Once the water runs clear into a bucket, you can put the outlet hose back in the sump and you're back in business.