About a year ago my PO4 was around 2.5. The problem is the phosphate gets bound up in the rocks and sand and leaches out into the water. A water change might give you immediate relief, but the rocks/sand are going to just release more until an equilibrium is reached. GFO and phosguard and similar products are good, but they only have a limited capacity to absorb phosphates. And they are relatively expensive. That is why some of us recommend LC. You can drop your phosphates a little at a time, every few days or so, until a relatively low equilibrium level is reached. Then swap over to one of the granular products to maintain levels. That is what worked for me (I did try GFO first, but at my levels it was spent very quickly). I'm not saying your approach will not work. Just be prepared to keep swapping out product. Of course this will depend on how big your tank is and how much rock and sand you have.