[tang daddy]

Even after changing the filters you are getting bad tds this is odd as the ro membraine would be stripping the water clean one would think....

I am almost 💯% certain it's your water that is adding to the phosphates, you may want to try to add some nitrates and carbon source "slowly" to see if it helps bring down the phosphates. As Warriorcookie has mentioned he had to add nitrates in order for his phos to drop down as they play hand in hand dragging each other down.

So if you only have a lot of one and none of the other then that's where the imbalance is and alsolock your phos where it is and not allowing it to drop lower. Rowa phos will cost you and arm and leg if you have to change it weekly.

Maybe try a brightwell bio brick and add some nitrates to help bring your phos down. You can also try reef biofuel and wet skimming as a carbon source. Any adjustments you make do it slow and watch your tank close for any I'll effects.