Let's start with your last statement:
Some nute companies "recommend" RO because of the high micronutrient content in some peoples tap will cause a toxicity when used with there high micronutrient products, but that does not mean it outperform tap water.
What, you just looking to argue about semantics here? Why the hell are they recommending it? You even said it. Tap can cause a toxicity, causing tap water to perform
worse. Not quite sure what your hang up here is. Look at what you just said dude. You just flat out said that is recommended because TAP WATER WILL FUCK UP YOUR MIX, causing nute toxicities (as well as lock outs).
That means RO will outperform tap, now doesn't it? Well, it does unless you want to get into some silly semantical argument. Have fun with that, if that is yo thang.
Before I get to some scientificy type stuff, I'll tell you that I would have to sit downn to figure the exact numbers, but I have grown over 60 strains of weed. I have had more than one 10,000W mother room holding well over 40 strains at any one time. I have also run 24 different strains, at one time, on a single RDWC system. I have used dirt, E&F, NFT, RDWC and have used both tap and RO water, as well as various nutrient regimes.
I personally have seen a lot of
Ca/Mg issues, both lockouts and toxicities, in my gardens and others. And they usually occurred with tap water. And the science shows us this should be of no surprise. The only time they ever occurred using RO is when I was running multiple strains, including heavy indicas and heavy sativas on the same res. But, YMMV.
RO water will always outperform tap, thats not true. Some people have stuff in there tap thats not good, but the majority is just fine to drink and grow with so how is RO always better??
You and I will have to agree to disagree on this one. If you have years of experience growing, years of study concerning plants and plenty of experimentation on top of that, you KNOW what the ppm levels of each macro/micro should be for both your particular strain and grow room. With tap water, you cannot achieve the PRECISE levels you want. There is the issue of alkalinity as well, which is not the same as pH. I'll get to alkalinity in a minute, but first a couple things in most tap water that you do NOT want to give your plants.
From one o' dem PhD fellas:
Fluoride (F) and chlorine (Cl2) are commonly added to municipal water at concentrations up to 4 ppm and can cause problems growing crops. Generally, high levels (above 1 ppm) of fluoride and chlorine can cause damage to the foliage (especially at the tip) and the flowers.
1 ppm is enough to cause a problem - that ain't very much, is it?
Don't be fuggin' up them flowers now, that is what we are after, after all, Sweet Lady Jane Flowers. I know you said you let the water stand. This is NOT as effective as some people think. It depends upon many, many factors. The first and most important of which is the source of the chlorine. I think most water treatment plants today are using chloramine as the source, as it is the trend. Chloramine is a combination of chlorine and ammonia. Chloramine will NOT evaporate out of water, nor does it have the 'chlorine' smell, so just because you can't smell chlorine, doesn't mean there is no chloramine in your water. Same thing for fluoride. It will NOT evaporate out of water either. CL2 is a gas at room temperature. Chloramine is not.
The only way to remove chloramine from your tap water is to actually add free chlorine to it so it begins to disassociate the chloramine molecule so the chlorine and ammonia can evaporate out, boil it (like in the distillation process) or use a carbon filter or membrane filter who's pores are smaller than the chloramine molecule on it.
A carbon and membrane filter like you find in RO units. RO units kick ass at removing chloramine. And good RO filter removes fluoride as well.
So, I could stop here, couldn't I? I've got a PhD cat telling you that chlorine and fluoride is TOXIC to plants. RO filters remove this threat, instantly making RO BETTER for growing. Always. Always. Always. A solution that does NOT contain molecules toxic to the plant will always outperform a solution that does, like tap water. But, there are more reasons, so I won't stop.
As side note, fluoride is NOT okay to drink. It is poison. Hitler and Stalin added F to the water supply because it subdued and made the prisoners more passive. So, your assertion that the majority of tap water is 'just fine' is not accurate. For either plants or humans.
The biggest contributor to tap water ppm is Ca & Mg. "Great! Mj needs Ca and Mg", you say. But not so fast. The calcium and magnesium in your tap comes in the form of calcium carbonate and magnesium carbonate. These two molecules are too large for the roots to utilize. Over time, they will break down, but until they do, not only are your plants not uptaking the calcium/magnesium carbonate, but those carbonates are locking out other nutrients, like K.
Calcium carbonate is CaCO3. It is also not very soluble in water, but is what usually makes up the ppm and need an acidic solution to disassociate. So, if your tap pH is above 7.0, the Ca in the tap in the form of CaCO3 is not usable by the plant. Before your plant can uptake Ca, the CaCO3 molecule must be broken down so you have a Ca2+ ion and CO3-. And your solution needs to be slightly acidic for this to happen. This takes time. This time spent is less impactful in dirt than hydro. To help break down CaCO3 in a hydro res, you need to add chelating agents like fulvic and humic acids and bennies.
This takes time. And it does take some energy from the plant. Time and energy better spent on growing than making Ca2+ available from a CaCO3 molecule.
So, before I get to far into it, the CaCO3 is not a molecule your roots can absorb, it needs Ca2+ for the exchange to occur. Further, the CaCO3 in your tap will inhibit the uptake (lockout) other nutrients while in that form. Same for magnesium carbonate. Yet that is the Ca you get in most tap water, CaCO3. Ca that needs further manipulation before it is ready for uptake.
As far as alkalinity, well, you get it plenty with tap water. Alkalinity affects how much acid you need to add to drop the pH. Tap water buffers really well, meaning you need to add more pH down then you want to. pH adjusters have cons as well as pros. The pro is getting in the pH range you want, the cons include things like pH adjusters are not good for your roots, they can easily fuck up a nute solution, they precipitate out nutrients you just put into your solution and they make you r solution more prone to a higher rate of pH drift.
I avoid pH adjusters as much as possible. With tap water, the alkalinity neccesitates that you use more acid than is good for your plants.
