You should really keep up with weekly water changes with newer tanks, especially once fish are added. It takes some time for NNR
to take hold and effectively deal with nitrates so the water changes are your best defence against nutrient build up. It also helps maintain a stable chemistry.
As for the phytoplex, you really don't need more than a capful a week if that. The star won't benefit from it much especially if it can be target fed. About all it will do for now is help the pod population some but moreso increase the possibility of nuisance algaes.