You should buffer plain RO if that’s what’s your using it can and will go acidic. I’ve done it all different ways and have settled on tap/ro<100 ppm.
This is what
@Mañ'O'Green has taught me about using RO cause my tap is extremely high PPM, ph, and high alkalinity
“The history of why I invented stabilizing RO. When I first started using RO It did all manor of weird PH shit to my reservoir when I added it to bring the PPM down in a nutrient mix to the range I wanted. I used RO because it added only water to the mix. But it took copious amounts of up or down to keep PH in range. You know that PH+ Nitric Acid adds nitrogen, PH+ Phosphoric Acid adds Phosphorus to your nutrient mix. When you use large amounts it will change your nutrient balance. Keep in mind I am in hydro and my PPMs would change by as much as 75PPM. This was not desirable. Then I learned that RO water is hungry and will pull Co² out of the air and drop the PH to 5.5 or lower. I read somewhere that adding some base ions would mitigate this action. It can be any metal ion. I started adding a little cal-mag to the RO and Bota Boom Bota Bang it stop hijacking my reservoir PH. Then I discovered that everything mixed better without any precipitation I could see if I used this "buffered" RO. The reason I used 50 PPM of Cal_mag was because that was the lowest number my EC pen could read. Not all Cal_mags are made the same but most are calcium nitrate and Mg nitrate and maybe some iron once again a source of Nitrogen I don't want. Hence my choice of Soluble Gypsum which is Ca and Sulfur, Epsom Salt is Mg and Sulfur. Cannabis can tolerate a lot of Sulfur way more than you are likely to get in any nutrient line. I settled on .3g Soluble Gypsum and .3g Ag Epsom Salt per gallon of RO that gets me close to that 50PPM mark that most meters can read. It works well for me so I teach it.”
