I’ve never done it. I just realized I’ve used my unit for the looooongest time and haven’t tested it. I just stuck a TDS meter in and it’s 076. Surely it’s way past time to replace the four stage filters. I have what’s probably a generic 100GPD 4 stage unit. Can anyone point me to what replacements I should pick up so I don’t order the wrong supplies? Pic below. So dirty, it’s scary. Not proud.

