Nitrates are between 2-5 ppm. Phophates are at 0. I'm never sure why the Phos is 0 as I don't run GFO. I only have a sump, skimmer and a golf ball size chunk of chaeto.Yes. Those two steps. Be sure when you are adding nutrients, (assuming your tank is low in the first place) that you are adding inorganic simple phosphate and nitrate. Heavier feeding or adding complex organics has lower success.
UV is helpful, however prorocentrum is less willing to go into the water. So after a few days you may need to do a short blackout in order to push more cells in contact with the UV.