almost giving up on the hobby

[Reefer Rob]

You definitely should have a TDS meter. Get the one that tests your water before and after your DI canister.

I don't see the size of your tank, but 2 tablespoons of GFO would be way too little unless the tank is a small nano.

If your nitrates are truly 0 with a reliable test kit you could dose amino acids to bring your nitrates up without raising PO4. This will allow you the remove PO4 biologically if your system has become nitrate limited.