Cut back on any frozen foods, or at least rinse them before use.
use only quality water like DI or RO/DI water.
Run a phosphate sponge for a few days, change it out if your readings don't improve with in that time.
You can also run a polyfilter that will remove much more than just PO4. good for alot of things.
Some PO4 removers have an affect on leather corals.
Thomas