There are two answers to your question.
If you are using dirt or promix or something like that your water is OK to use just add your food. Look outside is you garden green and lawn, yup see it's OK.
If you are doing hydro with ppm of 440 or so and most wells read different ppm depending on the season. Here's the rub, all manufactures directions for hydro are based on ppm zero so when they call for 600ppm in RO water that's what you get. You see RO takes all the bad and good out of your water. The other thing is you should never use just straight RO to feed your plants here is why
How to buffer reverse osmosis water
Here is a great tip for those who use reverse osmosis water to buffer your water and help stabilize pH. There are two ways, both efficient.
- For those who prefer simplicity, all you have to do is add 20% tap water to your reverse osmosis water.
- For the purists who do not want to use tap water, or whose water is particularly bad, here are two easy steps:
1 – First increase your pH up to 10.0 with
pH Up or potassium carbonate
2 – Then bring it down to 6.0 with
pH Down
In both cases you’ll obtain water well adapted to hydroponic nutritive solutions, while avoiding untimely pH fluctuations.
You need to raise pH first because the “buffer” elements have a very high pH or very low pH. You can start by adding acid, but then you will need pH up to raise your pH.
You need to buffer R.O. water simply because pure water has no buffering capacity. It is subject to big swings in pH every time you add something to the solution, making it unsuited for cultivation. Using pure R.O. is a classic source of failure.
If you’re using reverse osmosis water, add 50-100 ppm of Cal/Mg; this helps to buffer your water so nutrients absorb better. From Advanced Nutrients site
http://www.rosebudmag.com/hydroponic-tips-ideas/insider-tips-for-maximum-yield-in-urban-garden
What happens is that the basic/alkaline components (mainly calcium) that are responsible for the high PH (as in 7.3 or 7.6) also buffer it together with the more neutral components. As soon as you add SOME acid, the basic elements neutralize it in 24 hours, but loose some potency, respectively get eliminated partially within the "reaction". If you repeat that process, the alkaline components- and their buffer capacity get lower and lower until the alkaline buffer is "gone". The "last" time you add ph-down/acid to your water, it will drop drastically to perhaps under 5. This mostly happens when a week PH down is used repeatedly. With Nitric acid at 75 or 95 %, this will not happen, it will get the alkaline elements down in one shot. But that is the stuff that burns through concrete floors like alien blood and it's truly not everyone's cup of tea. If ever you can lay hand on it in the US without an explosive license.
PH of boiled water of 8.4 after 13 hours of boiling is "normal" because you evaporate lots of water, while calcium and other alkaline elements (already responsible for the high pH) remain in the water and hence will be present in higher concentration and push up the pH. There may also be some chemical reaction and transformation within these 13 hours of boiling, I don't know of.
Nutrients generally lower and buffer a certain pH, that's what any mineral composition with an acidic sum, added and dissolved in water does anyway. NUTRIENTS are actually made to lower the PH, as the usual 7+ is not suited. The only difference is that some manufacturers point this out explicitly while others don't. Some manufacturers may indeed add some more of specific components like mono potassium phosphate that helps lowering and buffering such Ph, but that's pretty much it. As a side effect (when running higher EC) you may have excessive Phosphorus that will result in Ca deficiency.
But in this context it is important to know that a higher nutrient concentration will lower the pH more than a weaker ratio. Hence in some cases it's not a bad idea to simply (slightly) increase the nutrient concentration by a click or two. It's also a reason why some manufacturers recommend higher concentrations as needed, and some commercial growers push the nutrient concentration higher.
If the PH of the base water is too high, most nutrients can't bring it down to around 6 and that's (only) where pH down- as in acids or other components are required. In ANY case it is always best to have, use or get water that is around and not (much) over 7.
RO water is fine, but take care what nutrients you use, as with some extra acidic nutrients (many are developed with areas in mind that have an excessive amount of calcium carbonate in the (well)water) you may end up with an unwanted but extraordinary low PH as well.
Attention, Ph and EC are interconnected, EC reading of a nutrient solution will not be the same at PH 5.0 as it is at 7.0!
