DIY PH down (using sulfuric acid aka H₂SO₄ or "battery acid")

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If you’re getting it from the auto parts store then it’s already diluted enough that anything less than prolonged contact (10 min or more) only leads to minor skin irritations in most. I myself don’t when notice because of the calluses on my hands. Once diluted further it might cause irritation if you soak in it for an hour. If you’re worried about pumps and the like the nutrient solution isn’t going to be any more caustic than it already is

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I’m using 96% sulphuric acid drain cleaner. The only thing I wished I had done earlier is to put it in a glass container instead of keeping it in the plastic bottle. After a few years it starts to gradually perspire through the plastic and now I have a ring etched in the shelf where the bottle used to be.

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gobbledegook

If I failed to explain myself to be understood properly, I apologize. If that is the case let me know and I will be happy to try to break it down more clearly. I will also provide links supporting the information provided if you wish. If you have other thoughts, let’s hear your take on it, along with the science to back it up - I am always open to new ideas.

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These threads are great, it’s like peeking behind the veil of all the fancy nutes we pay so much for. Thanks for doing them.

Is there something readily available that can be used for pure phosphorous?

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thanks much, I am glad you are enjoying the DIY threads, and I hope that they help save you some money so you have more to spend on seeds :monkey_face:

As far as phosphorous, fertilizer/soil pH controls much of the phosphorus availability to plants, so the best way to keep phosphorous available to your plant is to closely monitor the PH.

The Hammerhead and MOAB are both PK boosters you can make yourself for pennies.

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Interesting, thanks. The problem is I use mega crop which is already super high in K so when I add a PK booster I end up with way too much potassium and still not as much phosphorous as I’d like. I tried ‘treble super phosphate’, but it’s more of a lawn care type product and didn’t work for me. It seems hard to find just P without a bunch of K or N tagging along.

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Colloidal Phosphate aka Soft Rock Phosphate is a great source of phosphorous for your plants, since they can only take up inorganic phosphates. Down To Earth has a 0-3-0 Rock phosphate.
https://downtoearthfertilizer.com/products/single-ingredients/rock-phosphate/

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Killer, thanks!

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Thanks for the writeup. This is on my list of things to do still, but have been trying to use up what i’ve had laying around.

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well if you’re wanting to boost P then Phosphoric acid may be the way to go for ph down. How much P it adds I have no idea and when I’ve asked could never get much of a real answer on other forums. But it has to provide some sort of P boost.

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Phosphoric acid is useful for cleaning out clogged drip orifices in drip irrigation systems, but shouldn’t be used directly on the soil. The similarity of names such as phosphoric acid and phosphorous acid, and the reference of phosphorous in “NPK” may create some confusion about the content and effectiveness of these chemicals. It isn’t a good idea to apply phosphoric acid directly in soil as its strength is 45N, which can lower the soil pH to a value of 1.1-1.5.

For those looking to increase the uptake of phosphorous in their garden, in plants that are colonized with mycorrhizal fungi the ability of plants to utilize soil phosphorus is greatly increased.

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Oh I never meant to apply it directly to soil. I meant when used as a PH Down in solution. But never having realized there was a phosphorus acid, just always assumed phosphoric was the acid used to create phosphates.

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Yes, that is very different lol. Sorry for my confusion - I think @beacher was asking about something to add high amounts of P alone to his garden, so we may be talking about two different things at the same time. GH uses food grade phosphoric acid in their PH down - its the main ingredient at somewhere between 10-30%. For low amounts of alkalinity removal, phosphoric acid is a good acid of choice. However, it isn’t a good idea to add more than 2.25 fluid ounces of this acid to 100 gallons of water, because of the amount of P one would add. Also, Phosphoric acid is a lot more expensive than sulfuric acid, and tends to be less stable with much more drift.

As stated earlier, the most effective and widely used acid to lower ph is sulfuric acid; however, this is one of the most hazardous acids to use, so people need to be cautioned when using it in undiluted form. When concentrated acids are mixed with water, a tremendous amount of heat is generated (which can even distort or melt plastic). Improper mixing can result in bodily injury, which is why I posted so many cautions.

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Yep you’re right. I’m looking for a water soluble P only that is readily available to the plant. I do use phosphoric acid for my ph down which I’m sure gives a little P but i use so little I doubt it’s significant.

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I just ran out of ph down, and I went and bought some battery acid for $12.99 for 6 quarts. It’s all they had lol, and one gallon of distilled water. Followed your directions, take out 2 cups of water from the gallon, added 1 cup of acid. I’m letting it settle and mix on its own. Then I will test it out.

According to my math it should give me 24 gallons of ph down for $40. A gallon of distilled water is about $1.

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Concentrated sulfuric acid has a much higher specific gravity than water - meaning it is heavier and will sink to the bottom of the container. It is highly miscible, so it will eventually mix in on its own, but I would give it a stir just to be sure.

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I’ll give it a good shake.

Will it settle out over time?

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No. Once its mixed it will stay that way. Its just right after that initial pouring in thats any concern - and its really not a big a deal. Most times you will likely get enough mixing action just by moving the jug around, handling it, etc, to thoroughly mix it, but its still a good idea to give it a stir or shake.

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So I just used this diy ph down. In a 5 gal bucket of ph 7 water with mega crop nutes, it took about half a cup to bring it down to ph 6. The ph down is about 2. I’m not used to using that much to bring it down.

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