I'm guessing you don't live in the US? The EPA sets a limit of 10ppm due to health concerns (mostly long term exposure for youth).
To raise pH (and KH will always go up with it), you can use sodium bicarbonate which is also known as baking soda. This is both measurable and stable.
I'm curious why you would want to maintain an 8.2 pH though. Periodic water changes with the mixed RO will bring that down so gradually that nothing would be hurt by it if you wanted to lower it. Also, if you really want to keep GH / TDS the same, you need to add GH booster.
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To raise pH (and KH will always go up with it), you can use sodium bicarbonate which is also known as baking soda. This is both measurable and stable.
I'm curious why you would want to maintain an 8.2 pH though. Periodic water changes with the mixed RO will bring that down so gradually that nothing would be hurt by it if you wanted to lower it. Also, if you really want to keep GH / TDS the same, you need to add GH booster.
Sent from my Nexus 6 using Tapatalk