sorry to high jack the post. but Im using RO water as well with GH Flora series. my question is, shoul I mix calmag with RO even before the seed sprouted to charge the soil and buffer the ph? Im using a mix of 50% sphagnum 50% perliteYes at least at first because it is actually difficult to provide soluble forms of macros like calcium in the soil that assist with absorbtion of other nutrients. Good sources include composted eggshell and D-lime both of which take a real long time to break down and become available in the soil. I recommend general organic calmag+ because it is safe for living soil. After the harvest amend the soil with macros Dolomite lime, crushed oyster shell, and maybe some crab meal, composted eggshell, ewc, etc. It can take several recycles before you can totally forgo giving calmag with RO water but it will happen in time one day when your mix reaches the coveted “supernatural” status.
give them RO water during 3-4 weeks? Im gonna have to buffer the ph thenNo for seedlings just give them water for the first 3-4 weeks. The seed jacket has all they need til then. Plus without an established root system ph is irrelevant. If you are using nutrients anyway do you really need to use RO? Your tap should be ok unless it is high ppms...
Whatever water source you decide on yes you probably should ph adjust it once you do start giving nutrients (and calmag) with that kind of medium.