Lanthanum chloride for PO4 regulation

I'm surprised your PO4 is detectable with the Hanna. I think my setup is fairly similar to yours. I don't have a fuge either, and just run a 2-3" sand bed. Of course, besides from being one of those things that reefers tend to believe, I never actually really heard a good argument for why a DSB would be better at denitrification than a SSB. So , maybe just having a sand bed is enough. Although, I'm not sure why it would influence PO4 longterm, as benthic bacteria in the sand aren't exported readily? Could be something else though too idk...