I've been down this rabbithole myself. In my case the low nitrates and high phosphates were not effected by addressing the phospates at all. It was actually a product of underfeeding my system. It literally almost drove me out of the hobby. I tried everything, phosphate reactor/lower feeding/filter roller etc etc. I have a decent sized refugium that wasn't growing chaeto at all through all this. By upping my feeding to daily frozen/nori, it raised my nitrates which allowed the chaeto to grow which consumes both nitrate and phosphate. Now I have to feed the tank pretty heavy handedly to keep my nitrates between 2-5ppm and phosphate 0.03-0.05 ppm. Just my two cents and I admit without a fuge I'm not sure how comparable the situation is.