Ph control question
- Thread starter babynuka
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churchhaze
Well-Known Member
For hydro, the best pH down is nitric acid or phosphoric acid, and the best pH up is potassium hydroxide flakes.
For non-hydro, if pH is too high, it's probably because your soil was built with too much lime. If it's too low, built with too little lime.
For non-hydro, if pH is too high, it's probably because your soil was built with too much lime. If it's too low, built with too little lime.
churchhaze
Well-Known Member
The problem with baking soda is that it provides sodium instead of potassium. It is also a weak base whereas potassium hydroxide is a strong base.
This is one of the best deals you can get for KOH flakes.
http://www.essentialdepot.com/servlet/the-13/2-lbs-Potassium-Hydroxide/Detail
This is one of the best deals you can get for KOH flakes.
http://www.essentialdepot.com/servlet/the-13/2-lbs-Potassium-Hydroxide/Detail
Nullis
Moderator
Too much baking soda can indeed be detrimental, and stuff like that as well as pH Up/Down are short term solutions which are not ideal for soil growing.
Even with pH Up/Down, the pH of soil is going to fluctuate to some extent, and it is supposed to. Using liquid adjusters can actually lead to problems [in soil] instead of solving them. For one thing, there is no perfect pH for soil. Anything between 6-7 is fine. That doesn't necessarily mean 5.9 is bad, and it doesn't mean 7.1 is bad.
The pH of soil changes in the rhizosphere (root zone) as plants pump out ions to exchange for other ions, which include H+ (acidity) and bicarbonate (HCO3-, neutralizes acid). The manner it is influenced depends on which nutrients are in the soil and which are being absorbed (e.g. too much ammonium causes pH to drop over time). It is influenced by other substances that plant roots exude, as well as other organisms (i.e. microbes) living in the soil. Also, good soil has a "buffering capacity" which is related to it's cation exchange capacity. Quality soil has good CEC and buffering characteristics, which means it resists sudden changes in pH.
Some the materials most commonly used in potting mix tend to be acidic, such as sphagnum peat which can wind up harboring a lot of 'reserve acidity' as the exchange sites in the peat adsorb hydrogen cations (H+). As a result peat can have a low pH, or eventually revert to low pH if it isn't properly limed (liming restores base cations at those sites). Coco coir tends to have higher pH than sphagnum, but can still be slightly acidic.
The best solution for soil is to make sure it is well limed. Potting mix often comes limed, but may not have enough or be suitable for long-term.
Liming materials which are most acceptable include various forms of calcium carbonate (limestone, oyster, eggshell, crab meal) as well as dolomitic limestone which contains 6-12% MgCO3. Both calcium and magnesium are base cations, along with potassium. These are the most exchangeable cations (positive ions) in soil, and they are also essential plant nutrients. So liming provides minerals and neutralizes pH over time (long term). The higher the CEC of a given soil, the less frequently it requires lime (the more lime it requires at one time).
Typical rates (of pulverized limestone, oyster or eggshell) are 1-2 tbsp per gallon. These forms of lime are very forgiving and can't be easily over-done. Mix the liming material into the soil before planting in it.
How much you'll want to use exactly depends on the soil, liming material and your water source. Tap and well water in southern and western states may be very "hard" which indicates it already contains carbonate minerals. If the TDS of your water source is over 100 ppm (some sources are significantly higher) than there are very likely already carbonate minerals dissolved in your water (Calcium bicarbonate, magnesium bicarbonate), and such water will be alkaline. In these cases you probably don't need to lime, or wont need very much.
If you're using low TDS water (rain, bottled, reverse osmosis, multi-stage filtration) then you're probably going to want to use a heaping tablespoon or perhaps even 2 tbsp per gallon of soil mix.
Even with pH Up/Down, the pH of soil is going to fluctuate to some extent, and it is supposed to. Using liquid adjusters can actually lead to problems [in soil] instead of solving them. For one thing, there is no perfect pH for soil. Anything between 6-7 is fine. That doesn't necessarily mean 5.9 is bad, and it doesn't mean 7.1 is bad.
The pH of soil changes in the rhizosphere (root zone) as plants pump out ions to exchange for other ions, which include H+ (acidity) and bicarbonate (HCO3-, neutralizes acid). The manner it is influenced depends on which nutrients are in the soil and which are being absorbed (e.g. too much ammonium causes pH to drop over time). It is influenced by other substances that plant roots exude, as well as other organisms (i.e. microbes) living in the soil. Also, good soil has a "buffering capacity" which is related to it's cation exchange capacity. Quality soil has good CEC and buffering characteristics, which means it resists sudden changes in pH.
Some the materials most commonly used in potting mix tend to be acidic, such as sphagnum peat which can wind up harboring a lot of 'reserve acidity' as the exchange sites in the peat adsorb hydrogen cations (H+). As a result peat can have a low pH, or eventually revert to low pH if it isn't properly limed (liming restores base cations at those sites). Coco coir tends to have higher pH than sphagnum, but can still be slightly acidic.
The best solution for soil is to make sure it is well limed. Potting mix often comes limed, but may not have enough or be suitable for long-term.
Liming materials which are most acceptable include various forms of calcium carbonate (limestone, oyster, eggshell, crab meal) as well as dolomitic limestone which contains 6-12% MgCO3. Both calcium and magnesium are base cations, along with potassium. These are the most exchangeable cations (positive ions) in soil, and they are also essential plant nutrients. So liming provides minerals and neutralizes pH over time (long term). The higher the CEC of a given soil, the less frequently it requires lime (the more lime it requires at one time).
Typical rates (of pulverized limestone, oyster or eggshell) are 1-2 tbsp per gallon. These forms of lime are very forgiving and can't be easily over-done. Mix the liming material into the soil before planting in it.
How much you'll want to use exactly depends on the soil, liming material and your water source. Tap and well water in southern and western states may be very "hard" which indicates it already contains carbonate minerals. If the TDS of your water source is over 100 ppm (some sources are significantly higher) than there are very likely already carbonate minerals dissolved in your water (Calcium bicarbonate, magnesium bicarbonate), and such water will be alkaline. In these cases you probably don't need to lime, or wont need very much.
If you're using low TDS water (rain, bottled, reverse osmosis, multi-stage filtration) then you're probably going to want to use a heaping tablespoon or perhaps even 2 tbsp per gallon of soil mix.
I'll use Plagron light mix for soil and AN nuts.
I'm not familiar with that soil, and haven't used AN nutes. But, what I've learned is that if you're not overfeeding it won't take much ph adjustment. As nullis said, the soil has a tendency to hold the ph unless it's imbalanced in some way. Dolomite lime helps hold it higher if acidification occurs.
I think the common problem is for people to overfeed, which creates a higher ppm solution, requiring more ph up/down to move the solution's ph. The overfeeding leads to salt buildup, resulting in soil acidification, leading to using even more ph-up to adjust the already too-strong nutrient to a higher ph, to try and pull the soil ph higher. Becomes a vicious circle.
The only times I've read people being worried about which ph-up/down product to use is when they're organic. For you it doesn't seem to matter. But, if you follow the "less is more" principle for your nutrients, monitor runoff ph and ppm (for indications of salt buildup), and have 1-2 tbsp / gal dolomite amended into the soil, you might get by without even phing your nutrient solution. At least you'd need very little adjustment (meaning it would matter even less what you use).
I think the common problem is for people to overfeed, which creates a higher ppm solution, requiring more ph up/down to move the solution's ph. The overfeeding leads to salt buildup, resulting in soil acidification, leading to using even more ph-up to adjust the already too-strong nutrient to a higher ph, to try and pull the soil ph higher. Becomes a vicious circle.
The only times I've read people being worried about which ph-up/down product to use is when they're organic. For you it doesn't seem to matter. But, if you follow the "less is more" principle for your nutrients, monitor runoff ph and ppm (for indications of salt buildup), and have 1-2 tbsp / gal dolomite amended into the soil, you might get by without even phing your nutrient solution. At least you'd need very little adjustment (meaning it would matter even less what you use).