Reducing my soil pH

[Bond]

I've just tested my mix and its 7.2...which i believe is a little high for a grow medium.

What can i add to the mix next time i re-pot them to bring it down to the low 6's...which seems to be about what i should aim for.

Cheers in advance

edit: - The mix currently contains 25% Potting Compost, 25% Well rotted farm manure and 50% perlite.

 

[TGT]

I always add 2 table spoons or more of Dolomite Lime to every gallon of mix. This I find keeps the PH in an acceptable level and also makes the plants stay green longer into bud. Since using the DL with Promix soil I have not had any issues with PH. Just make sure if you purchase DL it has to be fine ground or better yet, powderized. Granuals will not start changing the PH till well after the crop has finished. Powderized works almost immediately. Hope this helps and good luck!

TGT

 

[Guest]

How are you testing the soil ph?I agree the use of dolomite can alleviate a lot of problems,I always use it.When I used promix,2 tbls per gallon,with ocean forest I used to use two but am finding 1 tbls per gallon to give me a slightly lower than neutral runoff while 2 tbls basically give me neutral runoff

 

[MTF-Sandman]

Dolomite lime will tend to stabilize the PH near 7.0...but it is alkaline so too much can make the PH even higher - neither are what you're looking for in this case.

Might wanna try some of the following to lower your PH:

Sawdust, composted leaves, wood chips, cottonseed meal, leaf mold, peat moss, lemon juice, PH DOWN.

 

[sproutco]

Add .75 pounds elemental sulfur per cubic yard. This would be 341 grams. 180 teaspoons per pound. 1/27 x 135 tsp = 5 teaspoons per cubic foot or 2/3 teaspoon per gallon of soil mix. :smile:

 

[inflorescence]

Dolomite lime is a buffer. Once the buffer has reached it's neutralizing capacity, whatever solution you water with, if less than 7.0 and contains no buffer of its own close to 7, will bring the pH down. Most nutes plus RO will be well below 7, more like 5.5, (PBP comes in at like 4.5 in RO) so a simple nute soultion will bring the pH down as long as you add enough to overcome the buffer. IE, if you add more buffer you gotta add more nute solution if you want to overcome the buffer effect and vice versa.
Also, I think I read that once the pH gets to 5.5 it takes a lot less pH down, or anything lower than 5.5, to drop the pH. In other words even without a buffer, a fixed amount of pH down will drop a 7 solution so many points but once you hit 5.5 that same amount of pH down will drop the solution more points than it once did.

 

[inuyasha]

use very little sulphur diliuted in water, have you used dolomite and if so how much of it?

 

[Guest]

I use coffee grounds. Irie, Bud

 

[Guest]

When using ph up and down,the PPM of the water is the biggest determining factor on how much up or down will be needed to effect a change in PH.Another words,very clean water will need much less ph down or up than very dirty water to effect the same change in PH.It may take 2 drops of PH down to get a 7.5 PH to drop to 6.5 with water having a 50 PPM reading whereas it may take a teaspoon of ph down to get the very same drop in PH with water that is 400PPM.

 

[Bond]

How are you testing the soil ph?

I've used a kit that i bought (can also test for N/P/K levels using the different chemicals provided). To do the pH test you add 10ml of soil, a bit of barium sulphate and add the pH soultion.

I've also got one of the probe type pH meters, that says the same reading as the chemical one.


As for dolomite lime, I did go looking for some at a gardening place but they'd sold out. I was under the impression that dolomitic lime raised the pH, but when i repot them i'll make sure i add some. Am i right in thinking that i'm looking the powdered stuff?

 

[Bond]

Sawdust, composted leaves, wood chips, cottonseed meal, leaf mold, peat moss, lemon juice, PH DOWN.

I'm liking where you're coming from man, does it make any difference what sort of tree the wood/dust comes from?

also, would this be in addition to the DL or instead of?

Cheers for the help people

 

[Ganja Guerrilla]

pine needles

known mulch for acid loving plants like azeleas

 

[vonforne]

Add .75 pounds elemental sulfur per cubic yard. This would be 341 grams. 180 teaspoons per pound. 1/27 x 135 tsp = 5 teaspoons per cubic foot or 2/3 teaspoon per gallon of soil mix. :smile:

you beat me to the correct answer. I was going to use your sig. link.


pine needles would work also if you steep them. Just as a soil admendment, they would take time to work.

 

[inflorescence]

When using ph up and down,the PPM of the water is the biggest determining factor on how much up or down will be needed to effect a change in PH.Another words,very clean water will need much less ph down or up than very dirty water to effect the same change in PH.It may take 2 drops of PH down to get a 7.5 PH to drop to 6.5 with water having a 50 PPM reading whereas it may take a teaspoon of ph down to get the very same drop in PH with water that is 400PPM.

Generally speaking this is true, but it's not always true and the reason why is carbonates.
Here is an image I highlighted from Big tokes.


You can see that Free Ca and Mg ions contribute to GH (general hardness) and to overall ppm (salinity) but that they don't contribute anything to pH (the green area) because they don't have an H ion to give up. Only the carbonates are able to take up acids (H ions) and they can therefore buffer a solution (the yellow area). So it's not total ppm that affects ph buffering it is only a small percentage of total ppm (the carbonates) that will effect buffering and thus will effect how much pH up or down you need to use.

 

[sproutco]

.

Also, I think I read that once the pH gets to 5.5 it takes a lot less pH down, or anything lower than 5.5, to drop the pH. In other words even without a buffer, a fixed amount of pH down will drop a 7 solution so many points but once you hit 5.5 that same amount of pH down will drop the solution more points than it once did.

:friends:

Originally Posted by the cult
i got a question for someone with good knowledge of ph and buffers, so i figured id take my shot here in this thread.

when i mix nutes and add ph down i take a reading with my metre, says eg 5.5 (approx where i want to be), im happy, i leave water for 30 mins, its risen to lets say 6.2, the effect of buffers in the nute solutions. i then add a drop of ph down, and take a new reading, its all of a sudden down at 4 something. how can this be? i dont understand the process. the buffering doesnt really change the ph of the water? it appears the ph was still at 5.5 as just a drop into the solution deals a total coupe de grace to the mix and i have to add fresh water in steps to get back up to the level i want to achieve.

can anybody explain how this works and what the buffers actually do?

and yeah, i calibrate my metre every week hehe

Once the buffers are gone from the nutrient solution and its sitting at a certain ph, you might find that just a drop of ph down drastically will change the ph.

Quote:
Titration
From Wikipedia, the free encyclopedia

Titration setup: the titrant drops from the burette into the analyte solution in the flask. An indicator present then changes color at the endpoint.Titration is a standard laboratory method of quantitative/chemical analysis which can be used to determine the concentration of a known reactant. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the titrant, of known concentration (a standard solution) and volume is used to react with a measured quantity of reactant (Analyte). Using a calibrated burette to add the titrant, it is possible to determine the exact amount that has been consumed when the endpoint is reached. The endpoint is the point at which the titration is stopped. This is classically a point at which the number of moles of titrant is equal to the number of moles of analyte, or some multiple thereof (as in di- or tri- protic acids). In the classic strong acid-strong base titration the endpoint of a titration is when the pH of the reactant is just about equal to 7, and often when the solution permanently changes color due to an indicator. There are however many different types of titrations (see below).

Many methods can be used to indicate the endpoint of a reaction; titrations often use visual indicators (the reactant mixture changes colour). In simple acid-base titrations a pH indicator may be used, such as phenolphthalein, which turns (and stays) pink when a certain pH is reached or exceeded. Methyl orange can also be used, which is red in acids and yellow in alkalis.

Not every titration requires an indicator. In some cases, either the reactants or the products are strongly coloured and can serve as the "indicator". For example, an oxidation-reduction titration using potassium permanganate (pink/purple) as the titrant does not require an indicator. When the titrant is reduced, it turns colourless. After the equivalence point, there is excess titrant present. The equivalence point is identified from the first faint pink colour that persists in the solution being titrated.

Due to the logarithmic nature of the pH curve, the transitions are generally extremely sharp, and thus a single drop of titrant just before the endpoint can change the pH significantly — leading to an immediate colour change in the indicator. That said, there is a slight difference between the change in indicator color and the actual equivalence point of the titration. This error is referred to as an indicator error, and it is indeterminate.

 

[inflorescence]

Back to reducing soil pH. The reason this is so much more difficult to get right than affecting pH in a DWC solution for instance is becuase if you use pure RO in a DWC it has no buffer and the solution will pH adjust to whatever buffer is in the nute solution you add to the water, generally for hydro this is ~5.5 for certain brands. The problem is if you conceptually think of soil or soiless as basically a soild form of DWC, well then CEC and whatever buffer is in the soil comes into play and thus your nute solution won't buffer to it's buffer of 5.5 like in RO DWC because of the interaction of CEC and buffers in the soil or soiless.

 

[TaprootErection]

Bond, dont use dolemite lime to reduce your pH. Lol. DL is used to neutralize your pH from soemthing low like 5-5.5

 

[inflorescence]

^Sorry, should have made myself more clear. I wasn't reccomending the use of dolo to lower bond's pH. I was using dolo as an example as to how and why acid-base buffer reactions work in soil so that he could have an understanding of what it would take to lower his pH and why it would work.

The mix currently contains 25% Potting Compost, 25% Well rotted farm manure and 50% perlite.

Obviously, the compost and/or manure is contributing to the high pH, and I actually don't know the buffer makeup of either so I don't know how much of a buffer strength it has. My point was, if it's just naturally alkaline to begin with, yet doesn't carry much buffer strength, it should be relatively easy to lower the pH with an acidic nute solution. Since a nute solution like FNG carries a buffer, the pH would eventually settle at whatever pH that buffers to. It may even be perferable to lower the pH in such a manner as to reduce shock as a pH drop of more than .5 a day can cause stress.

 

[Guest]

Why wouldnt dolomite lime lower a high soil ph?If the soil ph is 7.5 from the start and dolomite lime is added to the mix,isnt it going to buffer the soil to a near neutral ph?In essense it is lowering the soil ph.After the fact,I'm not sure the best way to lower soil ph,I know you can use all the ph down in the world and its not going to lower the soil ph,I've been there before.Hydrated lime is used after the fact if the dolomite is forgotten,but I've never used it and dont know much about it.I think using dolomite from the start would have alleviated his problem,but I wouldnt know what to do now

 

[sparobis]

i put a tsp of white vinegar to a gallon of water(tap) my ph is 6.3-6.8 never have nute lockouts.ect ect..i use the vial/dropper i buffer my tap water...put a half a vial..put 3 drops of the test liquid..i get that yellowish/green/puke color..im good to go!
peace
sparo