I have a liquigen 75 GPD rodi unit. I just bought and installed all new replacement filters from liquigen for the whole unit. After letting the system flush itself out for a few hours I tested the water with my TDS pen and it was reading zero. So I made 20 gallons of water for a water change and I tested the water once again and it was reading 34. I’m not sure why this is? It was reading zero for a short time and now it’s not. I was wondering... Is there something that I could add to this unit or should I buy a whole new unit? Anyone else have problems like this before?