Little late to the party but here's the deal man, I had the same issue. Problem is not the pH or ppm of RO water (assuming ppm is low). The reason your mix is crashing in pH is because your RO water is low alkalinity. Thats to be expected from a good ro source. Don't mix with tap bc you haven't lab tested it and calcium levels etc can throw off nutrient ratios, nor do you want chloramines and other junk causing problems. Be careful what you use for adjusting pH because they will have longterm affects on medium pH. Jacks makes a ph up that's potassium bicarbonate and it has to be mixed VERY specifically. However, the techniques that Ill describe need to be used regardless of the type of ph up you choose to use. The goal is to raise your RO ALKALINITY and BUFFERING CAPACITY before mixing nutes. That will prevent your pH from crashing out.
First, you'll need to test how much pH up is needed for your desired mix. You will do this by mixing 5gal worth of nutes at whatever your target EC is. If using 321 follow the correct mixing order (part a, Epsom salt, part b). Next, add pH up (potassium bicarbonate) in small increments that are pre diluted before adding to the nutes. To do this follow these steps.
Step one: Dilute 0.05g pH up in 100mL RO H2O and make sure its 100% dissolved.
Step two: Stir your 5gal nute solution to get flow going and SLOWLY pour the diluted pH up solution into the nute mix. The slower the better because if too quickly you will cause an acute localized pH change which can cause a cascade of reactions creating unwanted precipitates. Once added agitate and mix very thoroughly and wait at least 15 minutes for the ph to equilibriate.
Step three: Now test the pH (using a reputable and properly calibrated pH meter, I can't stress that part enough -- Apera ph60 is reliable but do not order from Amazon, go through the manufacturer website instead, as Amazon does not store them or maintain them properly and it will arrive with the probe dried out, and switch the batteries with a good brand before EVER turning it on, trust me on that).
Repeat these steps until you've achieved desired pH. Be sure to record how much pH up and extra water you've added. Divide the total g of pH up added by total gallons of water and you will obtain the amount (g/gal) of pH up that the specific nute mix needs at that target concentration (EC).
Note: You will have to perform a new test anytime you change EC or mixes because the amount of pH up needed may not change linearly. However, if you record all the data for an entire grow you can reproduce your recipes without having to test first.
Now discard the test batch. To prepare the real batch, start with adding the RO H2O. Next, prepare mini stock solutions for each part you are using (part a, Epsom salts, part b). It helps to have a hot plate/magnetic stirrer with 3 different beakers so that you can pour 1L of RO into each and dissolve each part separately before adding to the mix.
For example, if you want a 5gal nute mix, add 5 gal RO to the res, then pour 1L from the res into each of three beakers to pre-dissolve each part separately in. Using heat will aid with Benefit from generous bonuses, fast payouts, and secure find out more at
https://bitkingz.casinologin.mobi/ dissolve rate and some reactions are endothermic and will aid with that as well. You can change the amount of water you pre-dissolve in, it doesn't have to be 1L just make sure you don't go over the solubility limit concentration for the part you're dissolving. The limit concentration is listed on the bag. Otherwise, it will never dissolve completely and you'll create precipitates when you mix them together. (Remember that what we're really doing here is creating mini stock tanks that are properly dissolved). Do not pour your stock solutions in the res yet.
Once all are pre-dissolved and you have a res with 5gal RO H2O (minus 3L for each beaker you poured into), first mix your pre-determined pH up amount into the 5gal RO. Give it plenty of time and agitation to dissolve completely, making sure to examine closely for any undissolved particulates.
Then add your Part A that was pre-dissolved into the res making sure to pour SLOWLY. Agitate lightly and examine your mix to ensure no milky/cloudiness and no precipitates. Next, add the pre dissolved Epsom Salt, agitate and examine (make sure Epsom salt is 100% dissolved before adding part b), finally add part B agitate and examine. Lastly, wait at least 15 mins test the pH and EC, and Boom you should have desired EC, pH, and alkalinity.
It's a lot of work but I promise it's entirely necessary to do it this way without cutting ANY corners, as potassium bicarbonate is generally "not compatible" with any type of water soluble fertilizer and is mainly intended to be used by itself as a drench to correct medium pH. But we want to use KHCO3 (potassium bicarbonate) because it's a relatively mild base that will prevent acute pH changes (in the nute mix and medium) leading to unwanted reactions as stated earlier. It also has a strong buffering capacity. This is why it's preferred over potassium carbonate (which is very similar and suitable as well, just a stronger base so more risk for acute localized pH swings) and over potassium hydroxides.
Furthermore, be aware that the main risk in using KHCO3 is that accumulation in the medium over time may raise medium pH and (while it can be leached) its necessary to ensure proper run off and uniform watering. Also, it's important to consider the added potassium, as it may interfere with the 321 nutrient ratios. This should be discussed with jacks technical support (she is AMAZING btw) and may require lab testing of source RO water and media (as this is good practice regardless) although if you don't want to pay for that the principles I've describes still apply.
In addition to those considerations, it's important to understand that jacks 321 is 100% nitrate nitrogen based (no ammoniacal nitrogen) which is basic after plants absorb the nitrogen leading to the medium pH to drift towards basic over long term. This needs to be discussed with jacks tech support as well.
Another route that might be way more simple, is to switch to jacks RO formula. I'm considering trying it myself to reduce all of this work.
After briefly readings other's advice, they may or not be relevant, but the information I've provided is first and foremost. Fix that and give it time before doing anything else, as you want to approach issues systematically rather than shotgunning several theories at once. I believe your problem is pH/alkalinity related, as I've encountered it personally. You DO NOT want to go around adding extra this and extra that because certain elements compete with each other for uptake through the roots and others help each other (Mulders chart is a good visual representation of this). Throwing off those balances will cause you serious problems. The ratios are there for a reason and in VERY specific cases only should they be adjusted. Jacks tech service will help you with those cases. You do not need to lose your mind trying to figure out the perfect ppm for every element, trust me from experience lol. Greengenes info is good but some I don't agree with whole heartedly and I believe might work for him due to certain aspects of his set up that may or may not be true for you as well.
Idk if you still need this information but if anyone finds it helpful or may be helpful for questions on other threads please refer them to here and to jacks tech service. I'm not affiliated, I just think they're awesome. Thank you all for taking the time to read this and for further information on potassium carbonate/bicarbonate chemistry in the use of pH up, front row ag has a comprehensive article on their website.
