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I don't disagree with you but i'm stumped by this as I've made up a new batch of Ro water and currently reading 95-100tds and a gH of 5? I have ordered an API test kit to double check my results but i am very confused. I know people say you shouldn't chase TDS and focus on gh which is what i'm doing. Just stumped at how one of my tanks can be doing really well and the other one isn't with similar parameters. TDS meter has been calibrated with 342 solution and was bang on when tested.

I'm using NTLabs test kit , my old one expires and I've received a new one . Tds is around 105-110 and this is giving me a gH of 7 according to my test kit.

Well then, your GH test kit is inaccurate. You don't say which GH test kit is used. Most GH test kits are only an approximation. Take the API GH test kit for example. You drop the test solution into the vial until it changes colour. The drop size is inconsistent firstly. And secondly, what if it took 6.5 drops to change colour? It doesn't measure anything less than the whole number. So the measurement is a range ... if the colour changed at 7 drops, then the reading is between 6 & 7. What is your TDS reading?

Thank you. Sorry for the late reply. In reference to TDS then my gH is currently around 7 i know this isn't high but don't think my crystals like it this high. I am slowly bringing it down to 5. My question is i know 1 dgh is around 17.9 TDS how can my gH be higher than the tds in my tank? TDS is around 107 in my crystals. I've rematerialized my RO water to 98 tds and a gH of 5 .