How to use a buffering system to control the pH.

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Greetings Shaggy

Phosphate does the same, only that most phosphates are less soluble than citrate... anyway, why exactly do you want to buffer your stock solution?

Many inorganic/mineral fertilisers have a low pH not for the sake of buffering but because it keeps the phosphate and sulphate salts in the form of highly soluble dihydrogen phosphate and hydrogen sulphate, respectively. Additionally, low pH inhibits microbial growth... though it's highly impossible that anything could grow in a concentrated fertiliser solution anyway.
Bringing the pH up again once at it's final dilution in the rez automatically gives a buffered system as long as you have phosphate inside, no matter if you want to or not. Upping pH it's not about buffering but about a suitable pH for optimal plant growth. Using carbonates ain't perfect in hydro but would add a second buffering agent and adding again citrate salts would increase the buffering capacity even more and serves as microbial food too.
But that's just the theory.
In reality A) you don't have enough of these ingredients to really buffer much, B) plants take up phosphate, microbes use citrate, and bicarbonate/carbonate is lost to the atmosphere and change pH in much any direction, and C) temperature, dilution/concentration, and aggregation/precipitation further cause pH fluctuations. Bottom line is, you don't buffer your system unless you add excesses of one of the above things and that's not good at all (you might kill your plants). An alternative is the use of a GOODs buffer (MES, see your/my PDF) but that's not healthy at all. Better is to play with the composition and create a solution which "autocorrects" its pH during or rather due to assimilation, mineralisation (if you have organic compounds inside too), and root excretion and so on. An alternative would be to add ion exchange resin to the rez but that's quite expensive and might lead to a loss in trace elements. Growing in a high CEC substrate (e.g. soil, coco, vermiculite) instead of pure water culture does about the same without all the drawbacks . Or you use a drip line for the concentrated fertiliser solution in a DTW setup instead of a recirculating system and give a sh*** about proper buffering.
Back in the day I worked a lot with different buffers for different purposes (under others for cell culture) and I wouldn't use any of the things I learned on consumable plants or in open, dynamic systems such as hydroculture. There is probably no perfect buffer for hydro... there are a few possibilities but the good ones cost more than the doubtable benefit they promise (PS see secret PDF ).

Might not be the info you're looking for... figured I'd put it out there.

I'm a firm believer in growing with a full and cyclic pH swing. From 5.4 to 5.8 and back down again in roots-in type hydro and 5.6-6.0 in roots-out type hydro. pH goes up as the plants eat the nutrients, all the way to the top (healthy) pH. pH is then dropped back down to start by adding nutes again.

I only use r/o water and pH up, for controlling this swing. Zero pH adjustment required using pH up/down, after the initial res has been mixed.

edit: on a side note, all additional pH up/down added contributes to ppm I cannot fill out using food.

Do not bring ph down other than from ferts. Add ferts then adjust ph.

Soil or hydro?

I use oyster shells and minute ferts so things balance.

I never had ph swings in hydro other than adding ferts. Ph perfect with no swings is possible. I like citric acid and baking soda. Cheap and effective yet gentle.

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shaggyballs said:

My first goal is to achieve a PH stable stock solution.
Will a stock a & b type fertiliser solution have a tendency to remain PH stable over time all by it's self no buffering needed?

Thank you all again
Shag

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I've used only GH nutes with r/o water, for 15 years, and have found them to be rock solid stable. The pH and ppm changes are very predicatable. Ppm goes down, pH goes up.

Mix your res to a smidge below your target ppm. use pH up to bring it to the lowest healthy pH, for your particular hydro system. Top off daily with plain old r/o water, zero pH adjustment or nutes. As the plants eat nutes the pH rises. Once it hits the maximum healthy pH for your system, re-add more nutes to reach your target ppm and *gasp* your pH will be back to start.

Control how fast the pH rises with the size of your reservoir. Larger res is longer swing, smaller res shorter. It should only take 7-10 days for the full pH swing to happen.

Hydro is soooo simple when learned right the first time.

shaggyballs said:

@OO The reason I wanted to buffer my stock solutions was to increase shelf life by means of controlling PH swings in the bottle.
Are you saying there is no need to such a thing?
I guess I assumed this was a must for long term storage of a stock solution.

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In a tightly screwed bottle, there will only be pH changes if you have incompatibilities (i.e. precipitation). A mineral fertiliser with a low pH has a veeeery long shelf life if closed airtight.
Also, the pH in a concentrated salt solution is different from the final pH at a highly diluted concentration. There are just a few mineral/inorganic salts which require a neutral or alkaline pH for stability whereas most "fertiliser salts" do fine at a low pH or rather have an inherent low pH.
If you use organic stuff like amino acids then things look different .

I meant my rez or soil ph perfect with no swings. My experience has been that roots take in solution and don't either drink or eat but take in solution as a whole and never part. Yet for over 15 years i read people reporting their belief that cannabis roots can separately eat or drink. Roots ate more like an iv, take in solution at the rate and amount exposed.

I have tried stabilizing the ph of fert liquids for storage. It's terrible reactive and messy. Almost explosive. Like an ant acid in soda.

Now i have read that roots put negative ions back into soil. It takes a long time for ph to go down that way. Years long, so that shouldn't flux ph in a rez or soil grow for a long time.

Easy7 said:

I meant my rez or soil ph perfect with no swings. My experience has been that roots take in solution and don't either drink or eat but take in solution as a whole and never part. Yet for over 15 years i read people reporting their belief that cannabis roots can separately eat or drink. Roots ate more like an iv, take in solution at the rate and amount exposed.

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What nutes have you used with this effect?

When I mix a res with GH nutes, where the plant eats water/nutes in the same ratio, the health of the plants are not ideal. I get significantly better health and quality from a steadily rising pH, with a steadily dropping ppm. Same, every time, year in year out.

Pure blend pro, grow, bloom and soil. Maxicrop and microblast.

Just the basics with RO filtered UV sterilized water. Recirculating shallow water culture. Changing res out once a week. Topping off water and ferts 2x a day. PH'ing and exact fert top of % of exactly how much water topped. Never any sediment at the bottom of the res.

Easy7 said:

Changing res out once a week. Topping off water and ferts 2x a day.

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Well this explains why you don't see changes. Topping off with nutes *and* changing out your res every week? Wasting a lot of water and nutes there, unless your veggie garden is getting it.

I top off with pure r/o, always and the only changeout I do with my res is to pure r/o the last 3-5 days. Trust me, you want at least a pH swing.

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Having a varying pH means that your plants will have access to certain nutrients some of the time (say when pH is at the low end of the range), and other nutrients the rest of the time (say when pH is at the higher end of the range).

In my experience, keeping pH rock steady is usually asking for trouble, and a sub-optimal grow.

Douglas.Curtis speaks the truth.

No one wants to discuss how to stabilizes a hydroponic solution?