Just needing to know how to add ferts for a setup that has no plants except for a 30g plant filter full of Hygro polysperma....?

The setup is the main tank (40g, no Plants), Sump (40g, no plants), Plant filter(30g, Plant-only).

I have fully planted tanks and I understand the overall fert deal. What's confusing me is how much P and K and micros to dose for the plants to remain healthy and remove nitrates. If it was Just a 30g planted tank: I would dose 2ppm of P and about 20ppm of K. BUT its a 30g plant filter inside a 110g system ----So, how would I dose this?

TIA