Normal biopellet wont help much in reducing po4.
AIO is the latest one , which imo deal with both no3 and po4 veryvery effectively.
1 thing is , using rowa reactor like TLF or h20 brand reactor for aio pellet , wont work very well as they need to be tumble and are harder to timble as they are bigger and heavier.
Im using fr-45 and 3500 litr/hr pump to tumble my 1litre aio pellet.
If no space for biopellet reactor, just use biosphere with rowaphos lo . Dosing bacteria will help alotalot in reducing nutrient.
Imo biodigest/zeobak is muchmuchmuch better than mb7.