All I can really share in regards to biopellets and PO4 is that I was first interested in trying out the pellets because of their ability to remove both NO3 and PO4. I was a big time vodka doser, and haven't seen a nitrate in my tank for years and years, but PO4 was always an issue of me. I have never run GFO and always just tried to control my PO4 by natural means of feeding the right amount and doing water changes. Unfortunately I was dealing with those nasty brown corals that we have been stuck with at some point or another. A month after I first put the pellets online the color seems to shoot back into my corals and my PO4 levels shot way down. Its been almost 6 months now and my PO4 still seems to stay undetectable and my corals continue to look better and better each day. FWIW, the biopellets are all I run. I don't use carbon or GFO in my system...simply because I don't feel like I need to.
In regards to the question about how often to change them out. I was originally instructed by the manufacturer that I wouldn't need to change them out for about a year and so far, about half way there it doesn't look like I am going to need to add anymore anytime soon. This of course is tank specific and yours might be different than mine. Until I start noticing that the pellets are not doing their job anymore by means of testing for both NO3 and PO4 I will continue to have faith in them.
As a final thought, since this is sort of an update anyways. Aside from everything I just said...I am starting to have some algae show up on my rockwork, mostly green turf algae and I am also noticing some cyano on the sandbed. Really its not that big of an issue, but I don't know whether to blame it on the pellets or because my halide bulbs are overdue for a change. I am starting to notice about a 50/50 success rate among people who have used bio-pellets. I place myself among those that are satisfied and will continue to use the product because for me its working great. This is just a theory, but I have a feeling the pellets are working better in my system than in others because I am not pumping a ton of flow through the reactor. I use a maxi-1200 and upon glancing I can't even notice the pellets visibly tumbling. I think that a lot of folks think they need to see the pellets jumping all over the reactor and this may not allow them to settle enough to be beneficial in feeding the bacteria cultures in the system. Again, that is just a theory...
I find that ecobak really does not do a great job of lowering phosphate from elevated levels. However, I have found that once you lower your phosphate levels through other means, such as GFO, ecobak works really well at maintaining already low phosphate levels. I had extremely elevated phosphate levels. I reduced them via GFO/water changes and have had great success keeping them low without GFO or frequent water changes. I did wind up adding additonal ecobak to do so, but once I found my sweet spot in terms of the amount of ecobak to keep on line and pump flow rate my phosphate has remained low even without GFO or frequent water changes.
