For seedlings (I haven’t worked out clones on RO yet, that’s
@Gee64 specialty) you’re going to want to use bottled spring water or you’re going to want to build up your water a bit if it’s less than 50 ppms. One way of doing this is aerating dolomite lime like this and cutting it into the RO water
Or using bottled spring water or a decent dechlorinated ground water source and cutting it into the RO. If you use pure water (0-10 ppm) your plants will quickly tell you. My ppm meter was off by 30 points and it only took one watering of the seedlings for them to show me my meter was off, and this was when they were less than 10 days old.
You’ll read a whole lot of stuff that says “don’t feed your plants before 10-14 days” and while that’s trueish, it’s not completely true. When I’m told “don’t feed your plant” that means don’t give it anything. What they actually mean is don’t give it any fertilizers or NPK stuff. You still are going to want at least 50 ppms of calcium and magnesium in there which you can get naturally with fast acting prilled dolomite lime. I would recommend an organic calmag but if you’ve already come this far and are growing organic it’s much more beneficial just to run the dolomite lime water. Seedlings like it right around 65 ppms but 50 will keep them from being pissed off