Just a note on the ROWA, it is much finer than the Phosban. It's also suggested that it should fluidize more than the Phosban. Since it is fo fine, it takes a lot less flow to do so. It's kinda hard to adjust it correctly with the Phosban reactor I am running. Claims for this stuff read up to 7 months! It is also claimed that once it reaches capacity it won't release the stuff back into the water. Theoretically you could forget to change it and not worry about it.