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PHdown totally F-ing my nutrient profile in RDWC! Help

D

D350

Member
I'm running a 24 bucket RDWC under 9x600W with AK47,
now on 3rd week of veg, using RO water, Canna Aqua at 0,7EC and slowly rising up to 0,9EC. Also using Bacterial tea. Roots are white as snow.

Soon after 1st week Mg/Ca deficency started to show.
OK, no problem, did some research and Canna can be low on those. Added Mg and Calcium (Have them as seperate bottles) at ratio 3:1.
Of course, adding Ca (CaO) rises Ph a lot.

No problem, added Nitric acid to lower it. And then shit hit the fan with clawing and N overdose.
Research and thinking led me to N overdose by Nitric acid.
Started to add Phosporus acid for Ph down. Great, Iron def start to show (very likely P overdose).

What to do??
How can I lower Ph without totally screwing with my nute ratios?
Basically, as soon as you start to add Ph down, you have totally different ppms...

I made a table of how much N, P and S(Sulfuric acid) is added, when you are lowering PH down.

Note, all numbers relate to my res, in which i added 600ml Aqua A and 600ml B, EC of 0,7, Nitrogen ppm should be around 100ppm
Using
Sulphuric acid 5,5%
Phosphoric acid 59%
Nitric acid 38%
All marked as Ph-

AB has: 5.2% N. 2.6%P2 2.6% S.
Ph- has: 38% N. 59% P2. 5.5% S.
Ratio: 7.3. 22.7. 2.1.
amount added to efectively double the ppm of element:

For 2x ppm: 82ml. 26.4ml. 286ml.
for 10% 8.2ml. 2.6ml. 28ml.

If my calculations are correct, you easily add 50% or more of the element in question, trying to lower ph of ie normal water!
Basically, all nutrents with exact "scientific" ratios are worthless!

(Please, correct me, if my rough estimates are wrong.)

I think I may have to start using flower nutes, as I will be adding a lot of nitrogen?
Can use sulfuric acid? In my head it is the least problematic element?
Is there a Ph down, that has none of those and is safe for reservoir? (dont want another slime outbreak)

Please, chime in with suggestions, corrections...

Thank you
 
D

D350

Member
Just finished PH down water half RO half tap (EC 0,36) in the same res (Aqua AB at 600ml, 0,7EC)
Added all 3 acids, that I have for Ph down:
N-: 50ml which has upped my N ppm to 60% more
P-: 18ml which has upped my P ppm to 60% more
S-: 180ml which has upped my S ppm to 60% more

And my PH is still 6,0!!!
 
br26

br26

Active member
Phosphorus or phosphoric acid is probably what you meant is most commonly used as pH down. The unique effect it has is the disassociate in water 3 H+ atoms / one Phosphate molecule (PO4 (3-)). This differs from that of sulfuric or nitric, having respectively two and one possible H+ molecules for each SO4(2-) and NO3(-) nutrients. Therefore, the acidic effect of Phosphoric acid is triple that of nitric acid. But does not triple the pH, because it is log scaled.

Another problem with your calculations is the assumption that the phosporic acid is in P205 form. You have then taken the 43% of that number and made an incorrect percentile of P in total . The total P of H3PO4 is the correct percentile. Hydrogen @ 1.00 x 3 = 3.00g/mol Oxygen @ 16.00g/mol x 4 = 64g/mol , Phosphorus @ 30.10g/mol.

The correct conversion is 30.1/ 97.1 ~ 0.31

31% of 18 ml H3PO4= 5.58 ml of Phosphorus

How much water is in the system? 5.58 ml of P in a 24 bucket rez isn't much.

6ml of P in 189.5L (50gal) rez = 1,895,000ml : 6ml

189500 X (A) = 1,000,000

A= 0.52

0.52 X 6ml =3.1ppm increase of P

Check my calculations somebody, plz.

Why don't u stick to a proven line of hydroponic nutrients that work? Why play a guessing game? If you intend to mix and match, get your calculations correct. This is a science , not a fun lab experiment.
 
D

D350

Member
GreenhouseGrown said:
try using tap water instead of ro, solved my problems before.
Click to expand...

Yes, I went with 50%/50% tap/RO now, I think it is better now. I have a pretty hard water, EC 0.45-0.65.

I'm extra careful now with PH down.
Never before thought of that, could prevent many problems I had before
 
Q

queequeg152

Active member
Veteran
br26 said:
Phosphorus or phosphoric acid is probably what you meant is most commonly used as pH down. The unique effect it has is the disassociate in water 3 H+ atoms / one Phosphate molecule (PO4 (3-)). This differs from that of sulfuric or nitric, having respectively two and one possible H+ molecules for each SO4(2-) and NO3(-) nutrients. Therefore, the acidic effect of Phosphoric acid is triple that of nitric acid. But does not triple the pH, because it is log scaled.
.
Click to expand...



actually phosphoric acid (ortho), is considered to be considerably weaker than that of nitric acid. nitric acid is considered a boarderline strong acid, whereas phosphate is decidedly a weak acid.

the difference is one disassociates almost, or completely, where as the other, a weak acid, does not.

ortho phosphoric acid will not disassociate into three protons as you suggest, outside of fairly extreme circumstances.

you will notice that this acid has three pka values, having three 'OH' groups... basically this means that once one peals away, it becomes successively harder to peel another away.
its hard to explain why this is without sounding like an asshole.


again. nitric acid is far stronger than orthophosphoric, meaning you will use less of it per unit to drop the ph of what ever fertilizer solution you are working with.

hope this helps.
 
br26

br26

Active member
weak and strong acids only regard to Keq or Ka values. This is the disassociation constant of the [H+][anion] : [H-Anion] . This number has nothing to do besides the interaction of
water. How it is suspended in the solution regarding the ratio of broken down molecule to still intact, original molecule.

Use phosphoric acid for pH down. Sulfuric acid is problematic.

The RO system will also make your water more acidic after running completely through the system. Due to the limited ability for pH meters to read when the ppms are low, a true pH of RO water is difficult to determine. Although, if you look at the construct of the system, the semipermeable membranes allow for many of the anions and cations to become trapped at the opening of the filtering mechanism. These passages or openings are too large to stop the Hydrogen molecule or H3O+, which is the acidity without the additional anion you are looking for. Simply, RO all ur water if you wanna use less pH down in the end.
 
Q

queequeg152

Active member
Veteran
br26 said:
weak and strong acids only regard to Keq or Ka values. This is the disassociation constant of the [H+][anion] : [H-Anion] . This number has nothing to do besides the interaction of
water. How it is suspended in the solution regarding the ratio of broken down molecule to still intact, original molecule.
Click to expand...

huh? what are you saying?

weak acids do not disassociate completely in aqueous solutions, whereas strong acids do, or almost completely do. idk what you are trying to say.

a strong acid almost without exception, will will lower a given solution with a given alkalinity more than a weak acid.

also H+ is a cation, not anion. and lol at the H- anion.

you can use what ever mineral acid you wish, as long as the conjugate base is not toxic to you plants.
sulfuric acid will work fine provided you are not profoundly stupid in handling it.

i use HCl personally.... it being about 5 bucks a gallon.
 
br26

br26

Active member
H - anion means there is a bond....

lol, just here to burn me? How about the calculations? What do you think ? Sounds like you know your stuff.
 
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Q

queequeg152

Active member
Veteran
br26 said:
H - anion means there is a bond....

lol, just here to burn me? How about the calculations? What do you think ? Sounds like you know your stuff.
Click to expand...

no an anion is actually just a molecule or atom with a full negative charge. in other words its stolen an electron from somewhere.

im poking fun of the H- anion because to my knowlage it would be impossible to force a naked proton to hold two electrons? idk maby not.

the naked proton it self, the H+ does not even exist in aqueous solutions. the H+ notation used in chemistry is basically shorthand for H3O+. You wont see a naked proton until you get into like... fancy physics or plasmas etc.

anyway. regarding your calculations. i wont even venture a guess here. Its actually very difficult to approximate ph of complex solutions. with weak acids especially.
hell, just blowing bubbles through a straw raises the ph of a glass of water measurably.

what you can calculate is the concentrations of the conjugate bases, assuming they are of concern to you.
however, what you will find out, is that it takes quite a great deal of acid to appreciably effect the concentration of say, sulfate, or chloride, or nitrate even.
 
Q

queequeg152

Active member
Veteran
br26 said:
H - anion means there is a bond....

lol, just here to burn me? How about the calculations? What do you think ? Sounds like you know your stuff.
Click to expand...


i see now, i thought, initially at least you were trying to calculate the resulting ph of some addition of acid.
sorry i didnt read your post much beyond the errors i noted above.

what you are doing is very simple, with the only complicating factor being the dilution of your phosphoric acid.

do you know exactly the dilution ratio, or molarity, or density?
if not you would have to resort to measuring specific gravity/ density or something like that to make an approximation.

when you know the mass of phosphate per unit of volume, then just find the milligrams per liter, which i believe is the ppm approximation.

regarding me checking your math. there is no point, i would probably error just as easily as yourself. what i would reccomend is that you simply pound your data into saltmix.xls or any of the myriad other fertilizer calculators.

according to saltmix. 1 gram of ortho phosphoric acid, will yeild 79 mg/l phosphate per gallon.
 
J

jokerinthedark

Member
I normally use general hydroponics brand ph down for my dwc system. They claim use some ratio (unsure of amount) of phosphoric and citric acid along side mono ammonium phosphate. Granted I use single resevior dwc buckets for each plant. Hopefully this helps, stay frosty bro.
 
W

watts

ohms
Veteran
Not a straight hydro guy but I use phosphoric acid in my DTW reservoir. Very little is needed and it keeps the pH stable. Citric acid caused problems for me, in a reservoir.
 
br26

br26

Active member
queequeg152 said:
actually phosphoric acid (ortho), is considered to be considerably weaker than that of nitric acid. nitric acid is considered a boarderline strong acid, whereas phosphate is decidedly a weak acid.

the difference is one disassociates almost, or completely, where as the other, a weak acid, does not.

ortho phosphoric acid will not disassociate into three protons as you suggest, outside of fairly extreme circumstances.

you will notice that this acid has three pka values, having three 'OH' groups... basically this means that once one peals away, it becomes successively harder to peel another away.
its hard to explain why this is without sounding like an asshole.


again. nitric acid is far stronger than orthophosphoric, meaning you will use less of it per unit to drop the ph of what ever fertilizer solution you are working with.

hope this helps.
Click to expand...

No, the triprotic acid gives off more than one proton when reaching a target pH of near 6.0 in rez. While HNO3 is a 1:1 ratio for giving a Hydronium ion or H30+. The (pka1+pka2)/ 2 of Phosphoric acid (H3PO4) is 4.66pH. Meaning that, at above pH 4.66 it gives more than one H3O+ or H+ stripped off the molecule. This is not the entire solution, just a small portion that has two hydrogens released per phosphate molecule.

So, therefore, for each molecule of HNO3 , one H+ is released at pH 6.0. And with H3PO4, >1 H+ molecules are released at pH of 6.0.

Mass wise, to reach target pH of 6.0, less HNO3 will be used opposed H3PO4 because it weighs at 63g/mol . Phosphoric acid is 98g/mol.

But molecule wise, H3PO4 is more efficient. It also acts as a buffer system, It resides mainly as H2PO4- and also some HPO4(2-) when pH is 5.5-6.1.

http://ion.chem.usu.edu/~sbialkow/Classes/3600/Overheads/H3A/H3A.html
http://staff.buffalostate.edu/nazareay/che301/l4.pdf

:biggrin:
 
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F

Fishywater

Member
br26 said:
No, the triprotic acid gives off more than one proton when reaching a target pH of near 6.0 in rez. While HNO3 is a 1:1 ratio for giving a Hydronium ion or H30+. The (pka1+pka2)/ 2 of Phosphoric acid (H3PO4) is 4.66pH. Meaning that, at above pH 4.66 it gives more than one H3O+ or H+ stripped off the molecule. This is not the entire solution, just a small portion that has two hydrogens released per phosphate molecule.

So, therefore, for each molecule of HNO3 , one H+ is released at pH 6.0. And with H3PO4, >1 H+ molecules are released at pH of 6.0.

Mass wise, HNO3 will be less at 63g/mol . Phosphoric acid is 98g/mol.

But molecule wise, H3PO4 is more effecient. It also acts as a buffer system, It resides mainly as H2PO4- and also some HPO4(2-) when pH is 5.5-6.1.

http://ion.chem.usu.edu/~sbialkow/Classes/3600/Overheads/H3A/H3A.html
http://staff.buffalostate.edu/nazareay/che301/l4.pdf

:biggrin:
Click to expand...


......huh?... :biggrin:
 
Mister_D

Mister_D

Active member
Veteran
Your deficiency problem is related to you not upping the EC when your plants started asking for more (mag and cal def.). 0.7-0.9EC is what I'd feed rooting clones, and maybe the first week in a RDWC system, after that it gets bumped to 1.2-1.4 EC for the remainder of veg and flower. Throwing all these additives and various ph- in the mix has fucked up your nutrient profile. My suggestion is to drain the res, and refill with nothing more than canna aqua, and either phosphoric acid or sulfuric acid as your ph adjuster. Mix to 1.2EC and watch 'em take off :tiphat:
 
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