My 135 is very stable. I don't think the phosgaurd actually effects PH. The dust ids not very kind to corals though from what I understand. However I rinse well as the directions state.
Granular ferrous oxide comes by many names, phosban, rowaphos are the two that come to mind. These are best ran in a fluidized bed filter(phosban reactor) with very slow flow rate though it. But can be placed in any compartment in a bag, or pantyhose for that matter, where there is a decent flow rate through it.
Do some googling ......