Anyone have experience with acid pH adjustment on a commercial scale?

[OzBud]

Hi all,
I've got a bit of a work related problem (not cannabis related) and thought I'd reach out here to see if anyone might be able to shed some light on it for me. It's a bit long and technical but please bare with me, any insight would be greatly appreciated.

Here's a bit of background.

I work on a commercial strawberry farm growing strawberry plants/runners in coir bags on long 'tables'. I'm responsible for fifteen 50m (164') long poly tunnels covering 1 hectare (2.47acres). There's about 24,000 mother plants in total which need to multiply into 600,000+ daughter plants to meet customer orders.

We apply our feed from two 1000L (264gal) IBC tanks, we have a dosatron for each tank which injects feed tank solution into our raw water at a set injection rate which we raise or lower to get our EC in the desired range. Our company agronomist supplies a feed recipe based on an analysis of a raw water sample. The tanks have agitators in them so nothing settles out of solution, but no aeration.

I buffered the bags with a mix of Calcium Nitrate (150kg/1000L in tank A) & Magnesium Sulphate (75kg/1000L in tank B) until the runoff EC dropped to 1.0 then we planted away.

The day we planted we switched over to our vegetative feed recipe which consists of
Tank A per 1000L
80Kg Calcium Nitrate
20Kg Potassium Nitrate
1Kg Iron DTPA

Tank B per 1000L
25Kg Potassium Nitrate
35Kg Magnesium Sulphate
10Kg MonoPotassiumPhosphate
6Kg MonoAmmoniumPhosphate
1Kg Iron DTPA
510g Manganese Sulphate (20%)
15g Copper Sulphate
185g Zinc Sulphate
80g Solubor
10g Sodium Molybdate

Currently I'm working at an injection rate of 0.8% - 8ml from each tank per 1000ml of water which gives me an EC of 1.4

Ideally I'm aiming for a pH of 5.8-6.0 and here's where the problem begins.
A few weeks ago before we started trying to adjust our pH, our pH going in was 6.3 and the raw water just before it gest mixed with the nutrient solution was about 7.0.
I should mention we draw water from the local river along the edge of the farm which is filtered & slightly chlorinated (I think about 20ppm)
I've done a calculation using 10L of raw water, 80ml from tank A + B and it takes 0.06ml of 80% Phosphoric Acid to drop the pH by 0.1. I upscale it and add 7.5ml per 100L in Tank B (100x0.06ml + 25% because of our 0.8% injection rate) for every 0.1 pH we need to drop, as per the directions from our agronomist but it has no effect at all.
I've currently added 1900ml of Phosphoric acid to this batch of nutrients and nothing except the pH rising! Sometimes it will go down briefly but then a couple of hours later the pH is back to where I started or higher.
At first I thought it was some weird sort of reverse effect the acid was having due to some sort of unforseen reaction in the B tank, then I tested our raw water in my work area and in the last few weeks the pH has gone up to 8.4, so today I went & took a sample direct from the river and the pH was 9.0 and an EC of 0.12.

Can anyone tell me why no matter how much acid I add I'm not getting any noticeable results?
I've tried pouring concentrated acid in the B tank all in one go then giving it a good mix before letting the agitators take over.
I've tried slowly adding concentrated acid in small amounts and mixing thoroughly in between
I've tried diluting the acid first in 20L (5gal) of water and both pouring it straight in & pouring it in bit by bit and always stir it in thoroughly.
Every afternoon at the same time when the river pH seems to be highest I test the pH coming out of the drippers and then do my calculations and chuck more acid in the tank with no more luck than the day before.

Our agronomist isn't much help, he can't explain it and just tells me to keep adding more acid until I eventually reach the tipping point and the pH drops. The problem with that is if it suddenly decides to plummet I have to dump the rest of the tank because you can't try to adjust the pH back up.

I apologise for such a lengthy post, I'm just desperate for some sort of an answer. I appreciate and thank each of you who managed to read all of that and also anyone who may be able to help.

Thanks
Ozbud

 

[DrPhoton]

Have a look into water alkalinity, alkalinity is a measure of your waters ability to neutralize acids. It’s an important aspect of balancing pH levels. Often called a buffer in pools or aquatic environments.
If its too low, PH can fluctuate rapidly and be more sensitive to PH balancing chemicals. High alkalinity resists changes in PH, often creating high PH levels and makes it hard to bring down.

I will have a look into it more tomorrow if youd like, but i am no expert. Just plenty of experience with pool chemicals.

 

[D.A.A.S.69]

Hey OzBud, I'm not a scientist either, but what your agronimist,says to do is surely going to have some drastic effects on the strawberries before too long it sounds like to me.
I would try to filter that river water the best I could, if that doesn't help any, I would tell them they need to find another water source if that's possible. Even if I had to make some huge tanks to catch rainwater.
Sounds like you might get the agronimist job, an maybe better pay that goes along with it, if you can fix the problems, good luck with it, an I'm glad your back on GWE.

 

[Canyon Grower]

OzBud , I am a scientist but that doesnt mean I will be of any help here. Im not a chemist, but thats what you need. My opinion is that you heve something in your original solution that is acting as a buffer. Its "soaking" up your acid in disproportionate amounts, preventing it from making small incremental adjustments in PH. The danger here is that you are in a very sensitive chemical environment. Sort of like going over a cliff. You adjust again and again with little to no result and then boom you have the opposite effect. Your agronomist is probably going by a "recipie" and isnt likely to provide you a solution. Best of luck !

 

[growmore]

OzBud I work as a consultant in the hydroponic cucumber sector assisting growers who are having problems like yourself. This is not really a topic for discussing online, as it is a complicated topic and without knowing your general knowledge on this subject it is difficult to know where to start. I can see 4 main areas where you would be encountering problems, which I will try to explain. This should be simple for an agronomist to fix if they specialise in this area and if they don't they should not be giving you advise.

I buffered the bags with a mix of Calcium Nitrate (150kg/1000L in tank A) & Magnesium Sulphate (75kg/1000L in tank B) until the runoff EC dropped to 1.0 then we planted away

Normally you would not buffer coir this way. The reason you buffer coir is to remove the sodium that is naturally occurring and replace it with calcium and magnesium. The method, you used does work but is a really bad way to achieve this. Calcium Nitrate And Magnesium Sulphate are both water soluble but when you mix both together you naturally form a new compound which is Calcium Sulphate which is not soluble and no longer available and becomes problematic

The tanks have agitators in them so nothing settles out of solution, but no aeration.

Tank B per 1000L
25Kg Potassium Nitrate
35Kg Magnesium Sulphate
10Kg MonoPotassiumPhosphate
6Kg MonoAmmoniumPhosphate
1Kg Iron DTPA
510g Manganese Sulphate (20%)
15g Copper Sulphate
185g Zinc Sulphate
80g Solubor
10g Sodium Molybdate

Firstly you should never add Micronutrients in an un-chelated form, when mixed into a stock solution. 510g Manganese Sulphate (20%), 15g Copper Sulphate, 185g Zinc Sulphate. These Amounts seem excessively high for these compounds and more like you would use, if they were in the chelated form. Please check and let me know what they are?
If your tanks are agitated then it is not recommended to mix any compounds that have Phosphorus and Magnesium in them in a concentrated amount. The Phosphorous and Magnesium combine to form Magnesium phosphate, which is not soluble and their for not available to your plants. This reaction is quite slow and by doing this you will always see changes in the Ph
You are correct when you say that nothing settles out of solution but that is only because you are keeping it in suspension with agitation. It does not mean you do not have any insoluble compounds present and if you were to turn off the agitator then you would see a participate form on the bottom of the tank.

I hope that helps with the simple problems In regards to the answers about Ph, these are quite complicated and if you want more info just let me know before I go into it in more detail. I have made several comments about PH on this forum and I have found that people assume that they know all about Ph and are not open to learning or listening if it doesn't agree with their thoughts about this subject.

Our agronomist isn't much help, he can't explain it and just tells me to keep adding more acid until I eventually reach the tipping point and the pH drops. The problem with that is if it suddenly decides to plummet I have to dump the rest of the tank because you can't try to adjust the pH back up.

This comment is totally wrong " The problem with that is if it suddenly decides to plummet I have to dump the rest of the tank because you can't try to adjust the pH back up." You are making a statement about this so if that is what you think please give your reasons why you think this?