Thanks 
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I saw that too. I take it to mean that if you mix up a certain quantity of buffer - like your 0.01M solution - it will buffer a specific amount of added acid - lets say again 0.01M of acid - it wont matter if that amount of buffer (number of moles) is mixed into a 1 liter jar or a swimming pool. It will still buffer the same exact amount of acid - measured in moles. In other words - its the molarity that counts, not the size of the container or the dilution rate.
On another note - Ive been reading and now Im confused again - or still 
It looks like you are using the acid form of MES all by itself as a buffer, but I was just reading on some of those links above that they are using the acid form of MES mixed with the salt form of MES to create the buffer. I assume this is the āconjugate saltā thing.
So, MES can work either way or? Im still very vague about this whole weak/strong/acid/base/salt conjugate thing. Now you see it now you dont?
Im not even sure what my question isā¦ hmmmm could be the pills I guessā¦ 
EDIT: Love the new graphs! My new question is - has anyone run across any references to how strong a solution of MES is safe to use? I have not seen anything on that yet. I am assuming āsafeā doses would be a matter of PPM rather than molarity, so we should be able to dilute the stuff and still have it work - maybe?
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Yes, precisely.
Molarity refers to the number of moles per liter of solution. The way it was stated is somewhat ambiguous. When the volumes are undefined, itās easier (in my mind) to get a handle on this by simply using moles or grams. Volume really doesnāt matter, then. Or, say something like 100ml of 1M solution. But, I guess thatās how chemists think.
That is an option.
When we think of buffers, we are thinking of a weak acid or, perhaps, a weak base as the primary constituent. A weak acid will partially de-protentate and come to an equilibria with the solution. De-protenate meaning, gives up an H+.
This is the MES acid:
This is the conjugate base:
Note the difference between the two. MES acid give up an H+. Once it does that you have itās conjugate. This is the BrĆønsted definition of an acid / conjugate. Thatās it!
Letās look at some more:
Acidā¦Conjugate Base
H20ā¦OH-
NH3ā¦NH2-
H2SO4ā¦HSO4-
Baseā¦Conjugate Acid
H20ā¦H3O+
OH-ā¦H2O
H2NCONH2ā¦H2NCONH3+
Under BrĆønsted:
If a molecule contributes H+ to solution itās an acid. Once it contributes the H+ to the solution it becomes the conjugate base of itās former self.
If molecule wants to absorb an H+, it is the base. Once it absorbs the H+ it become a conjugate acid of its former self.
Now letās talk strong / weak.
A strong acid will readily want to give up itās H+ turning itself into a weak conjugate base. The weak conjugate base derived from a strong acid is relative stable and doesnāt strongly attract H+ ions. What this indicates is that the interaction of a strong acid in solution will tend to favor conversion into itās conjugate base form. It gives up all of itās H+ ions.
A weak acid doesnāt āasā strongly give up itās H+ ions but when it does, the conjugate base is likewise formed. The conjugate base may attract H+ ions to convert back into the acid form. An equilibrium is created between the acid and itās conjugate depending on the concentration of the acid and the quantity of H+ ions in solution. The amount of the weak acid and itās conjugate base will vary as a result.
So, what this is saying, by having the MES acid in solution, you already have some of itās conjugate! How 'bout that. Albeit small. By adding more conjugate base, the effect is to alter the ratio and force a shift in the PH. The underlying Ka, pKa remains the same. The point of equilibria is the Ka value (or pKa value when thinking PH).
Alternatively, if we add some OH-, we deplete some of the H+ freely available. The weak acid will try to maintain itās equilibria by then giving up more of it H+ ions (pulling the solution to a more acidic state by neutralizing some of the OH-). This is the buffering effect.
The chemistry nomemclature is as follows:
HA = weak acid.
A- = conjugate base
For a solution containing a weak acid and itās conjugate base, the reaction is as follows:
HA + A- ā A- + HA
e.g. nothing happens, they happily swap back and forth between an acid and conjugate base.
If we add a strong base (OH-) to the solution:
HA + OH- ā A- + H2O
We convert the strong base into the conjugate base and water. Since the OH- is consumed, the PH change is slight.
How about a strong acid:
H+ + A- ā HA
The conjugate base reacts with the strong acid converting it into the weak acid.
A salt of the conjugate, in essence, is the addition of an atoms/metal to the conjugate forming a stable compound. A conjugate salt when added to a solution will disassociate into the conjugate and the metal.
For instance:
Acetic Acid (acid) ā¦ Sodium Acetate (conjugate salt)
CH3COOH ā¦CH3COONa
Here is an example of PH adjustment using a strong base as opposed to it conjugate salt: https://www.goldbio.com/documents/3550/MES+Buffer+0.5M+Stock+Solution+with+table.pdf
That would be my current understanding on how this stuff worksā¦
I have paged through some papers on MES concentrations and, for certain crops, no detrimental effect. Other crop, they see a detrimental effect when exceeding certain concentrations.
Stabilization of pH in solid-matrix hydroponic systems.b4d64c4bbeda07241088152de2dab332e873 (1).pdf (83.5 KB)
2-[N-morpholino]ethanesulfonic acid (MES) buffer or Amberlite DP-1 (cation-exchange resin beads) were used to stabilize substrate pH of passive-wicking, solid-matrix hydroponic systems in which small canopies of Brassica napus L. (CrGC 5-2, genome : ACaacc) were grown to maturity. Two concentrations of MES (5 or 10 mM) were included in Hoagland 1 nutrient solution. Alternatively, resin beads were incorporated into the 2 vermiculite : 1 perlite (v/v) growth medium at 6% or 12% of total substrate volume. Both strategies stabilized pH without toxic side effects on plants. Average seed yield rates for all four pH stabilization treatments (13.3 to 16.9 g m-2 day-1) were about double that of the control (8.2 g m-2 day-1), for which there was no attempt to buffer substrate pH. Both the highest canopy seed yield rate (16.9 g m-2 day-1) and the highest shoot harvest index (19.5%) occurred with the 6% resin bead treatment, even though the 10 mM MES and 12% bead treatments maintained pH within the narrowest limits. The pH stabilization methods tested did not significantly affect seed oil and protein contents.
An evaluation of MES (2(N-Morpholino)ethanesulfonic acid) and Amberlite IRC-50 as pH buffers for nutrient solution studies.
All buffering agents used to stabilize pH in hydroponic research have disadvantages. Inorganic buffers are absorbed and may become phytotoxic. Solid carbonate salts temporarily mitigate decreasing pH but provide almost no protection against increasing pH, and they alter nutrient absorption. Exchange resins are more effective, but we find that they remove magnesium and manganese from solution. We have tested 2(N-Morpholino)ethanesulfonic acid (MES) as a buffering agent at concentrations of 1 and 10 mol m-3 (1 and 10 mM) with beans, corn, lettuce, tomatoes, and wheat. MES appears to be biologically inert and does not interact significantly with other solution ions. Relative growth rates among controls and MES treatments were nearly identical for each species during the trial period. The pH was stabilized by 1 mol m-3 MES. This buffer warrants further consideration in nutrient research.
Evaluation of buffer toxicity in tobacco cells:
Borgo_2017.pdf (792.1 KB)
Havenāt gone through the literature thoroughly. Beat me to the punch. Keywords, for instance, Hydroponic MES buffer.
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Almost forgot to respond to this - yes, I think it does. The main reason is that this thread isnt so much about Mega Crop specifically as it is about buffering in general. Mega Crop just happens to be the focus nute.
Anything we learn here should be applicable to any nutrient you use if you are wanting better control of the PH in the solution.
At least, I hope so
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All of that helps - but Im going to have to go through it a few more timesā¦
Thanks!!
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Ok, decided to look at the citric acid instead of the phosphate buffer for the moment.
The formulation of MC is using mono-potassium phosphate as a primary ingredient which is the weak acid component of the phosphate buffer weād be interested in. The conjugate is dipotassium phosphate and is a base. In order to increase the buffering capacity against the upside, weād add more mono-potassium phosphate to formula. The feeling is the quantity needed would throw too much potassium and phosphate into the solution. So, Iām going to defer this for the moment to think about it.
Hereās a look at a citric acid buffer calculated to 20mM in the 500ml MC solution. I donāt know the plant safe amounts for the citric acid and itās conjugate. And, Iām guessing that this concentration is likely exceedingly high. An interesting note is that the previously observed precipitates at high PH are not noticeable until >9PH with this solution.
edit: updated graph to add titration of 5mM citric acid in 500ml MC solution.
edit: updated graph to add titration of 10mM citric acid in 500ml MC solution.
edit: normalize starting point on graph to PH4.
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Still trying to decode this, but it looks to have some good info.
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At first look, the citric acid doenst seem to be nearly as effective as the MES - by a lot.
So, is this a single buffer element or did you also add the conjugate base to the citric acid?
So far, it looks like all these tests are with the acid component only rather than mixing acid with conjugate base or salt?
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Yes. There is a significant difference. We are on the far end of the pKa for citric acid while for MES we are closer to the pKa being in the middle of the range for the PH weād want.
Oh, and I really have no idea of what is a safe amount of citrate buffer would be. The only references that indicate concentrations that I have found so far have to do with soil remediation and plant uptake. They are using citric acid applied to the soil in that case. For that, it appears the concentrations were higher than what weāve tried here. So, I could use some guidance or thoughts from anyone who may have experience with citric acids in a hydro-solution. One thing is for certain, a citric acid buffer is not to be used in an Aquaponics set-up.
Ahhh, but the conjugate is already hidden in there
HA + OH- ā A- + H2O
I was not looking to āpreā adjust the buffer PH since we are doing a titration curve on the slurry. In essence, we are making the conjugate on the fly! Three KOHās produces potassium citrate + H20 as the conjugate, I believe.
Hence, this is one of the reasons Iāve deferred looking at the phosphate buffer. For a phosphate buffer, the weak acid is the mono-potassium phosphate and the conjugate salt is dipotassium phosphate. MC already has the weak acid in the formulation. By adding the conjugate base, all that weād be doing is moving the PH more basic. We arenāt adding more buffer capacity to the upside by doing this (downside is a different matter but we are already starting off acidic). In order to add more capacity, weād have to add more mono-potassium phosphate. Perhaps this is why MC notes that theyāve increased the buffering in V2 by the addition of additional mono-potassium phosphate?
I think this is what we are looking at (with the arrows being bidirectional between the acid and base)
acid(HA) ā¦ conjugate (A-) ā¦ conjugate salt
KH2PO4 ā KHPO4- +(H+) ā K2HPO4
I may try some pre-PHāed buffers that are a combination of a phosphate and acid such as a phosphate-citrate buffer to see if there are any significant differences.
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More new stuff to process. Thanks!
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Iām following along, if thereās anything I can do to assist just let me know. Ur grasp on chemistry is much stronger than mine
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Ahhh, well, figuring it out as I go my friend. Thoughts are certainly welcome. And, if you have some of the MC version 2, any observations that you have would be interesting!
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I never worked with mc v1 but the smell of v2 is, well, strongā¦
Once I bring myself to open the bag Iāll let ya know.
I have a NBC respirator around here somewhereā¦
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Iāve added a low concentration MES titration at 0.000854M and 0.002M free acid in conjuction with MC (v1) at a 1.7EC.
See the OP for the plot of the titration curve and the transfer function.
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I see the new plots and notes in the first post. Very very helpful!
So, am I thinking about these formulas correctly?
Is it ok to call these x multipliers a slope or buffer factor or ratio? So, 2.9903 would be the slope of the plain MC graph, and 2.2407 would be the slope of the Megacrop + 0.852mM MES?
Then, adding the 0.852mM of MES to plain MC increases the buffer factor by 2.9903/2.2407 = 1.33
Does that mean that if the PH in my rez with plain MC is going up say 0.5 PH in 12 hours, that adding 0.854mM of MES would extend that to 12 x 1.33 = 15.9 hours?
And if I added MES at 2mM concentration, the time for that same 0.5 PH increase would go to 2.9903/1.3363 x 12 = 26.8 hours?
P.S. You are putting in a lot of time, thought, and spending a significant chunk of change getting us this information. This is way above and beyond. I have not seen anything even vaguely close to this amount of information, at this level of detail and with this quality, clarity of presentation by anyone ever on any of the forums. Im talking about the theoretical background info and explanations as well as the data collection, graphs etc.
This thread needs to be a FAQ.
Thank you sir!!!
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The equations are just straight line approximations of the PH titrations between 5.6-6.5 using the ubiqutous y = (m)x + b. (m) being the slope, (x) being the independent quantity of KOH, (y) being the dependent PH, and you can for the most part ignore the intercept (b) when looking for rate of change differences.
While not tied directly to time, if everything else between the two remains the same, then that should work out as youāve described. At minimum, there most certainly should be a slowing of any PH change. PH is logarithmic, so Iād have to twist my mind around this to figure out how a pre-existing time based problem would come into play. Iām unable to do so at the moment
Received the ion exchange resins, will try these when I have some free time.
Lol. If there is a purpose, Iāve just been given the excuse to explore things that Iāve also been curious about. Similar to your documentation of your HPA experiments (and copper).
I do hope that these types of exploration on OG will expand and help contribute to our collective knowledge and discussion no matter how itās applied. And, I hope others will feel encouraged to do the same. Whether success or failure.
edit:
This ion exchange resin appears quite slow to react to changes in the OH- concentration. From the way this is acting, Iām thinking that in practice there would need to be an initial preparation stage to get the PH of the resin somewhere near the target PH before placing into the final solution (initially quite acidic). The initial stabilization appears to take a bit of time but it may be improving on subsequent step changes.
This will take a bit to get figured out. Iāll need to restart this titration and drop the amount of resin in solution down somewhat. I started out at a fairly large amount of resin and will scale this back to the suggested 1g/gal. This looks like itāll a bit more lengthy of a titration and I may need to revise how I collect the data for this one.
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Excellent. I just replaced some plumbing parts, cleaned, and re-filled the system. I couldnt do a really thorough cleaning because I would have had to leave the roots with no mist for too long, but I can already tell that made at least some difference. My MES will be here in few days, so that will give me a new baseline for comparison.
That was fast! I am really eager to see how the resin compares.
Im curious how you are doing this physically. That resin is listed as a fine powder. Did you just add it to the liquid or is it in a bag or filter or?
Im not at all sure how it gets prepped before use. The only thing I read was it can be re-conditioned by a rinse, and soak in acid. I dont have any real details though, so no clue how long to soak or the PH of the acid needed or if the type of acid makes a difference.
Iāll see if I can find anything specificā¦
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Yes, fast to receive. Explains the expense to some extent. Cost, ~$1.30 per gram delivered.
Iām just adding it to 500ml of RO + MC and stirring the entire concoction. That is for the titration curves. Not for practical use. What you would see from this is a curve would be based on the optimal solution contact with the resin.
The CG-50 is quite fine and would probably not work well in a filter bag. It may work in a ācolumnā or an in-line style filter with a small screen size. It is really intended for columns, I think. You do get lots of surface area, conversely.
Found this from the Jay Frick, et. al., āStabilization of pH in Solid-matrix Hydroponic Systemsā paper:
For resin bead incorporation strategies, Amberlite DP-1 (cation-exchange resin beads, 16 to 50 wet mesh, 8.1 meq/g; Sigma) were first conditioned, pH-adjusted, and nutrient loaded as in Barta et al. (1990). Conditioning involved slow column elution with 20 resin bed volumes of each of the following solutions in sequence: 1 N HCl in 3% (v/v) aqueous methyl alcohol, 1 N NaOH, 1 N HCl, and 10-3 M Ca(NO3)2.
For pH adjustment, resin beads were soaked for 48 h in a KOH solution, with KOH concentration dependent on desired pH and ionic strength of the nutrient solution. The nutrient-loading step included another column elution step with highly concentrated (10Ć) Hoagland 1 nutrient solution. Major cations included K+, Ca+2, Mg+2. and micronutrient cations.
The Barta paper is entitled, āPreparation and use of weak acid resins for pH control in plant growth media and soil-less culture systems.ā I have not found an on-line copy of this paper.
So, it seems as though they are pre-loading the cation and anion sites along with adjusting the PH of the beads (as a starting point). This may not be as complicated as it sounds and could be a simple as having the beads sit in a concentrated PH adjusted nutrient formulation prior to adding it into the system. But, idk. Would need to get into the theory of how these resins work to develop a protocol.
This is a plot from the data while Iām getting used to how this stuff acts:
The CG-50 is the red curve. The other curves are the various MES concentrations.
The CG-50 is relatively slow to stabilize and because of that I decided to call it stabilzed when the meter shows 1/1000 of 1 PH stable for > 2 seconds or so. At around PH of 6, I changed that to let the solution stabilize for >45 minutes per point. Thatās where you see the PH drop. When itās stabilized, it does seem to stay fairly stable only moving several hundredths of 1 PH overnight. This is without any pre-conditioning steps on the CG-50 and a relatively large amount of the resin (500mg).
Iām going to restart this today with a smaller quantity of the resin and along with longer dwell times.
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Very interesting. Im going to have to review that graph a few times I think. Im not at all sure how to interpret whats going on as far as telling if the resin is ābetterā than the MES for our use.
The MES 0.005M and 0.010M plots are both flatter than the resin plot.
Wait - I just realized the three higher concentration MES plots and the resin plot are not covering the same range as the lower MES mixes 5.6-6.5? On the other hand, the resin looks to have similar ābuffer capacityā to the 0.01M MES and almost as good as the 0.02M MES.
That higher capacity is a good sign, especially since you did do any pre-conditioning.
On the other hand, that preconditioning makes me hesitate a bit. That plus the probable need for some sort of inline column filter has me hesitating a bit. Im not sure how to integrate something like that into my system without a fair amount of trouble. Iāll have to think about that part a good bit.
I have not had time to do any more looking for info/details on how to prep or condition the resins. I wonder if we could email the author of that paper and see if he would forward a copy to us? I will put that on my list of things to doā¦
Here is a quote from that HydroBUddy guy who recommended using the resins in hydro to control PH.
Ion exchange resins are insoluble and the only thing they need to be efficient is to have solution passed around them all the time. So it is simply a matter of putting the ion exchange resin in a place where fresh passing solution will be in contact with it all the time - like inside a filter connected to the irrigation system - and thats it, no more pH problems, no more additions to control pH, problem absolutely solved.
and then this as far as re-conditioning.
However not ALL ion exchange resins work. Particularly the type of resins that work well in hydroponics are weakly acidic cation exchange resins and their effect has been studied extensively on several peer reviewed publications. If you want to use these resins in your hydroponic system you need to buy the commercially available Amberlite DP-1, Amberlite IRC-50 or the more recently available Amberlite CG50. You would need about 1g per gallon of solution you wish to control and you should place the resin in an inline filter - those used for drip irrigation are great - to achieve the desired pH control levels. When the resin stops working you simply need to take it out, wash it place it in dilute hydrochloric acid (your average pH down solution will do), then wash it again, to regenerate its surface and prepare it for another crop.
I just noticed that point. The HydroBuddy guy in the link above recommends 1 gm/gallon, so your initial testing was almost 4x higher concentration. On the other hand, he says to get longer duration of PH control, you just need to add more resin.
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Iāve titrated a solution containing Megacrop along with 132.3mg of CG-50 ion exchange resin.
The overall titration was monitored in 10 second intervals. Each addition of 100uL of 1M KOH would be added after allowing the solution to stabilize to some extent. The point where I considered it to be minimally stabilized was at 1/1000th of 1 PH unchanged for 40 seconds. As you note in the stabilization plot below, the true time to stabilize is quite lengthy and I was not interested in waiting the many hours per point.
The entirety of the titration over time looks as follows:
As you might notice, stabilization of the PH in the solution containing the CG-50 is a very slow process as the resin slowly exchanges OH- ions with H+ ions. Also notice, the CG-50 without any preconditioning acts acidic when first added into solution.
An example of the time to stabilize a step change in OH- ions:
The titration of the solution as compared to MES looks like the following:
The dark blue plot is the āamountā of CG-50 as suggested by others for use in hydroponics (1g/gallon = 132mg/500ml).
From the linear equation produced, the suggested amount might have a similar effect as that of 2mM MES. Whether or not the CG-50 will continue to absorb OH- ions up to the capacity of the resin at any one PH is not clear to me. Though, the rate (speed) at which the OH- ions are absorbed does appear to be a function of the solution PH.
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