Thanks Alex,
are you sure your phoshates at 0.1 ppm? If you are sure, so your silicates at top. Believe me. Think of adding RO unit, if you are going to have SW tank for a long time. Tap water contains not only phosphates, silicates and nitrates. There a lot of poisonous stuff, heavy metals. These things won't make ypur corals happy. What you can do now is to put Phosphate/silicate sponge to remove whatever you have now, but after water change it will unfortunately comeback. I don't think adding fighting counch will solve your problem forever.
Thanks again!!!