Yes you should get your phosphates up to.03- .1. I keep mine at the higher end. Your diatoms are depleted, you won’t see them again unless you add silicates.
This is a dumb question, but i was using a cheap squeeze bottle to add some AB+ and reefroids a few weeks ago (feeding corals + trying to boost P). That is the only thing (outside of adding direct P).
Is there a chance that it could have been leaching silicates? Unless there was/is something else adding silicates that I don't know about (RO water has 0 TDS).