Been buying ro from various shops for a while but never thought about asking what the TDS reading was. I asked at one shop today and it the guy told me there's is 6.7 I always thought you should be getting 0 TDS, is that not right ? The guy seemed to know what he was talking about, he showed me the ro unit, and said they changed the filters when the tds goes over 10. He also says that this area as bad tap water, so he reckons that the other shops will have similar readings. I have been suffering from a lot of algae, could this be the problem ?