I've not used either of those product, usually phosphates come from your source water. What are you using to mix your SW
with and top off with? I would test your source water for phosphates. If you are getting readings on a phosphate test that means you are getting it from somewhere.
If you are not getting it from your source water then I suggest more frequent PWCs and see if that corrects the situation before you start adding things to the tank.
Phosban is a good product as well, though I haven't used it either.