Alright, so i tried the sand thing - filled up a cup full of RO water , poured some sand into it, mixed it up. Its been about half an hour, and its rather white and cloudy. Holding it up to a light, its got both white, yellow, and green sediment free-floating, so i guess its the sand!
I've been using "Black gold" brand sand.. guess i won't be doing that anymore. Grrr... thought it was a good thing to do. I'll look for a different sand then.. any suggestions?
Just bought a TDS meter - one didn't come with my RO unit.