Yes. The problem is your system does have phosphates but they are being consumed by the algae. Effectively taking them out of the water causing a very low readings. They are still getting into your system. The cure is to find the source of the phosphate. Often it is food or the source water. As long as the algae is growing there is phosphate in the system. You might consider a GFO reactor. It does reduce phosphate significantly. There are many brands out there. I use the one made and sold by bulk Reef supply. Once I started using it the algae in my tank stopped growing. It is still there but isn't looking too healthy.
It is always a good idea to rinse frozen food in RO water before you feed it to the fish. I use a small plastic strainer that I got at walmart for less than $1 to thaw it in then rinse it quickly.