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Old 06-14-2015, 03:55 AM #31
The.Cook
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Quote:
Originally Posted by blueberrydrumz View Post
hey,

basically if i wouldnt break the buffer of my tap it would slowly rise towards 7 ... so i was asking if using a lot of P2O5 to take the water down to 4.5 to break the buffer and then bringing it back up to 5.5 will unbalance the water and maybe in the end unbalance my feed water?
Or will that be the case anyway as we want a acidic solution of around 5.5... and it doesnt matter how i get to 5.5 as H+ and OH- will never be in equlibrium in the feeding water as we are shooting for 5.5?
hope im getting my point across hehe
thx
@blueberrydrumz]

K maybe I got your point... Not so easy to explain but... Kinda interesting...

ok so,
pH=-log[H+] (for example pH7=10-7 H+)
while pOH=-log[OH-] (so pOH7=10-7 OH-)
also, pH+pOH=14 so if pH=5.5 than pOH=8.5 no matter how you get there.
So, if by "unbalanced" you mean different concentration of H+ and OH- yes, otherwise you would be at pH7.

BUT, the 2 path are different in terms of substances added to water so of course there must be some difference when when you finally reach pH5.5

It's related to buffer, I'll try to explain.
so, P2O5 reacts with water giving H3PO4 wich is a strong acid. It has 3 dissociation levels (it can release up to 3 H+ ) so I'll use HCl instead just to make it easier.
Also, water has many ions acting as buffers so I'll use a classic "chemistry classroom" example of acetic acid in balance with his ion.

Basically a buffer is just something that can "neutralize" both OH- and H+ that are eventually added to a solution. So lets suppose we have a solution with acetic acid (CH3COOH) and its ion (CH3COO) at the same concentration of 0,1M

CH3COOH + H2O = H3O+ + CH3COO-


To calculate corresponding pH we use that formula:

[H+]=Ka([CH3COOH]/[CH3COO-]

because we said they are at the same concentration of 0,1M, H+ concentration will be equal to Ka (dissotiatiom factor of the acid) and pH will be equal to pKa, in that case 4,74.

If we add 0,01M of HCl, it will react with acetate

CH3COO- + HCl → CH3COOH + Cl-

Note that HCl has dissociated in H+Cl- but H+ bonded with CH3COO- so H+ concentration didnt raise because of them.

At the same time, 0,01M of CH3COO- reacted with HCl so CH3COO- concentration will be 0,10-0,01=0,09.

Knowing new concentrations and Ka we can calculate new pH with the same formula as before
[H+]=Ka([0,11]/[0,09]
in that case will be 4,66 just 0,08 lower than before. Consider that adding the same amount of HCl to pure water would bring pH from 7 to 2 as 0,01M HCl would mean0,01M Cl- and 0,01M H+ . 0,01 = 10-2 so pH 2

Obviously, everything said above is true (at his countrary) in casr a base is added

CH3COOH + NaOH → CH3COO- + Na+ + H2O

If you keep adding HCl (or NaOH) it will react with CH3COO- (or CH3COOH) till there will be no more left.

So, going back to your question, you will always end with the same pH of 5.5 so same concentration of H+ and OH-, but you will have a lot more PO4--- (and other dissiociation forms too) along with the ion of the base you use to raise it from 4.5 to 5.5

I know its kinda complicated but I cant explaine it better than that

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Old 06-14-2015, 05:23 AM #32
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Originally Posted by dr-dank View Post
Thanks for the thoughts guys. The cook has it. I sometime test with pure RO when I have a new batch of coco. Yet to see higher than about 200, which I assume is pre-charge, so I don't flush.

I feed the same 6/9 ~ 650 PPM every day. All plants get the same, until last week when just that plant gets water.

I don't think evap answers this as I do the test within 5 minutes. Mix nutes, ph, measure ppm, water, collect runoff, measure ec.

If I had barely any runoff I think this would make sense. But as noted I get an average of 50%, which one would think would balance out the ions.

That said.....

It is hot/dry here. I am in somewhat small pots and some do get a bit light by the next water. Perhaps its the transpiration that explains the increased ion concentration. Still, if that were the case you might expect nute burn or as a symptom I could drop feed strength.

But 6/9/650 PPM under a 600 W in a 2x3' area already seems a bit low....

Regards
its not the evap of the run off water. its the evap of water in the medium.

u can try n drop the feed. but as u said its not being overfed, its being dryed out. So same nutes, just less water, making them more concentrated.

What I would do in this situation is feed more often. this to me, is actually one of the big advantages of coir. Being able to utilize a small amount of medium and feed it more often, to get results that would compare to 3 times the amount of soil per plant.

and on the amount of runoff. If u got 10%, instead of 50%, my guess is ud see a even higher level of salt buildup. So instead of trying to reset the medium with so much runoff every watering. just water more frequently, with less runoff, ur gonna love what happens to the plants when u do this.
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Old 06-14-2015, 03:34 PM #33
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thank you for taking your time to explain.. i have to reread a couple of times but im starting to understand.. concentration of H+ and OH- are relative and equal at the neutral point at Ph7
what gets really complicated for me is understanding how H+ and OH- react with the cations and anions in the feed solution
so, this is going to be long but..
how would you go about working out a nutrient formula based on a ideal ionic balance
with for example the ideal water - RO
i take it you would have to take into consideration that the plants need more of some nutrients at certain stages as others,
knowing high concentration of calcium can lock out magnesium & potassium
high concentrations of N interfere with potassium
higher level of magnesium contributing in phosphorus uptake etc.
as well as other synergistic correlations of some nutrients
wouldnt there be a demand for different formulas for different growth stages:
Veg
Pre-Flower
Stretch
Bud Set
Bud Growth
Bud Ripening

Last edited by blueberrydrumz; 06-14-2015 at 04:16 PM..
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Old 06-14-2015, 08:04 PM #34
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Originally Posted by Miraculous Meds View Post
its not the evap of the run off water. its the evap of water in the medium.

u can try n drop the feed. but as u said its not being overfed, its being dryed out. So same nutes, just less water, making them more concentrated.

What I would do in this situation is feed more often. this to me, is actually one of the big advantages of coir. Being able to utilize a small amount of medium and feed it more often, to get results that would compare to 3 times the amount of soil per plant.

and on the amount of runoff. If u got 10%, instead of 50%, my guess is ud see a even higher level of salt buildup. So instead of trying to reset the medium with so much runoff every watering. just water more frequently, with less runoff, ur gonna love what happens to the plants when u do this.

I tend to agree with this. I used to auto-water 3 x a day but went to dtw top feed. I am sure using the same volume but twice a day would help.

Isolating the runnoff would also shed some light.

Attached is the latest victim, sly og. I did not flush this one much, so this is with full strength @ 1.4/650 PPM after about 9 weeks.
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Old 06-14-2015, 09:13 PM #35
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Quote:
Originally Posted by dr-dank View Post
I tend to agree with this. I used to auto-water 3 x a day but went to dtw top feed. I am sure using the same volume but twice a day would help.

Isolating the runnoff would also shed some light.

Attached is the latest victim, sly og. I did not flush this one much, so this is with full strength @ 1.4/650 PPM after about 9 weeks.
hard to judge from just one pic, but i would say i can see a couple of problems:
1. looks like overwatering... leads to nr.2
2. couple of nutrient deff prob cause you are more or less flushing with every watering with 50% runoff, it stresses them too
3. heat stress

so i think biggest prob is the watering, i agree with miracle meds, more feeds less water, around 10% runoff but 15% to be on the safe side cause of the high heat.
what i have observed is that if the coir is too wet nutrients cant be properly absorbed.. that would coincide with my overwatering theory
2-3 waterings with lights on and a very short watering in the night with around 5*C ambient temp difference between day & night is perfect
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Old 06-15-2015, 12:02 PM #36
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Dear The.Cook,

You are awesome.

Love,
Paperchaser825
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Old 06-15-2015, 10:07 PM #37
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Quote:
Originally Posted by blueberrydrumz View Post
hard to judge from just one pic, but i would say i can see a couple of problems:
1. looks like overwatering... leads to nr.2
2. couple of nutrient deff prob cause you are more or less flushing with every watering with 50% runoff, it stresses them too
3. heat stress

so i think biggest prob is the watering, i agree with miracle meds, more feeds less water, around 10% runoff but 15% to be on the safe side cause of the high heat.
what i have observed is that if the coir is too wet nutrients cant be properly absorbed.. that would coincide with my overwatering theory
2-3 waterings with lights on and a very short watering in the night with around 5*C ambient temp difference between day & night is perfect
Thanks. Need to mull this. I agree with the heat. I have a 600w in a 2x3 closet. Passive/massive airflow. Run lights at night and this is a hard time for them.

I did not think you could overwater an established plant in coco. More so I would not think that 10 or 90% runoff would matter if what goes in is a balanced/full feed, as is my case.

I do agree that more watering sessions, or a larger pot is better for me. Some do get light on the daily schedule and I know that makes things wonky in the media.

Also, this is a plant that is harvested so I expect them to look a bit off. They should be dying after all. This would look far worse with a flush.

FWIW, I am going to give blumats a try.

Also, I ran a test where I watered 2 x, and measured the runoff on the second. It was still higher than what went in, but only by ~ 100 ppm. I think this is showing the theory on evap in media has merit.

Regards
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Old 06-16-2015, 12:53 AM #38
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Quote:
Originally Posted by dr-dank View Post
Also, I ran a test where I watered 2 x, and measured the runoff on the second. It was still higher than what went in, but only by ~ 100 ppm. I think this is showing the theory on evap in media has merit.
Cant get your point...
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Old 06-16-2015, 02:20 AM #39
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Just to be clear....I understand I should not be adjusting my pH based upon runoff, but are you also saying a nutrient solution pH of 7 is nominal? Please advise kind sir.
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Old 06-16-2015, 04:47 AM #40
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Cant get your point...
sorry. To be clear.

rather than the once daily, I did a test where I split the nute solution and watered twice, measuring the runoff from the second watering to the input.

I typically see 200+ higher, this time it was only 100 higher, and so closer to the input solution.

So as was hypothesized it was not the lack of runoff volume I got, but a lack og watering frequency that lead to evap in the coco and resulting increase in ppm. Thus at the next water I would see the higher ppms on the runoff.

Honestly my plants are too big for these containers and even 2x a day is not enough. Hence I am going to try the blumat approach. I like the idea and am so cramped for space bigger pots are hard to work in.

Regards

Last edited by dr-dank; 06-16-2015 at 05:56 AM..
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