one of those britta filters will bring your ppm down to 80 or so, i have the same thing at my house, they ph is 8.1 with a ppm of 256 roughly, i use a britta faucet top filter and it brings the ppm down to 7.2 or so which is still to high, dont be afraid fo ph down, it wont kill your plants, if your in a pinch squeeze half a lemon if a gallon of water and it will give you 5.5 roughly