Hi I’m having a bit of trouble with my RO from Colin’s water products. I think it’s a 350 gpd. Anyway it was producing water the very best and then the TDS crept to about 3. So changed the resin (unger) and it persisted to remain at 3. Changed the pre filter and still it remained around 3. The next step was the resin must be off so ordered tulsion. Changed the resin and it’s coming out at 1. Why isn’t the resin doing the job and bringing it to 0. Any ideas in what the problem might be ?