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

You can easily make your own PH down solution for much cheaper than you can buy in the store. You can make a gallon for around a dollar. BE SURE TO FOLLOW THE DIRECTIONS CAREFULLY TO AVOID INJURY WHENEVER DEALING WITH CHEMICALS

Note: with all of that being said, sulfuric acid that you get as “battery acid” is considered safe to deal with, just don’t be stupid. I know that at first it can sound scary or off-putting at first to think about dealing with sulfuric acid, however it’s actually pretty benign in this form, and is also beneficial to your plants.


Buy some H₂SO₄ aka sulfuric acid at your local auto parts store - it is around for 7 or 8 dollars, and is enough sulfuric acid to last you several lifetimes. They don’t usually keep it on the shelves, so you will have to ask them for some “battery acid.” The sulfuric acid you will buy at the auto parts store is most likely 33%, which means its already diluted. Pre-diluted sulfuric acid is marked as battery acid/fluid meaning it has already been diluted. However, we are going to dilute it even more to around 1.65%.

Pour off 2 cups from a gallon jug of distilled water - DO NOT USE TAP WATER - IT IS UNSAFE TO MIX WITH SULFURIC ACID.

Put on some safety glasses and some rubber gloves and pour 1 cup of battery acid in to your jug of distilled water with a funnel and let it sit for 5 minutes to naturally mix, and then put the top back on the
gallon jug and gently shake to mix. If you get any on yourself be sure to wash it off.

Never pour water into an acid - always pour acid into water. IF YOU POUR WATER INTO ACID IT MAY BOIL OVER AND BECOME UNSTABLE

Some people like to add one or two drops of natural blue food coloring to their homemade PH down solution so nobody will drink it accidentally.


Sulfuric acid is relatively safe to handle, as long as you take precautions, and don’t drink it. Mechanics and wine makers use H₂SO₄ it all the time, and it is safe to use. Phosphoric acid is derived from sulfuric acid. Orchards and berry gardeners and potato farmers commonly use sulfuric acid.

Sulfuric acid provides sulfur in the form of sulfate, which is essential to plants and is often low in available water sources or fertilizers. High rates of sulfuric acid do not cause any issues with crops.

As mentioned, DO NOT USE TAP WATER - tap water may contain trace amounts of copper, which when mixed with sulfuric acid creates sulphur dioxide which is a highly toxic gas.


As with any other PH down, you wil have to test it yourself with your water and nutrient solution to see how much you need to lower your PH to the proper level.

If you have a remote hydroponic reservoir you can pour the 33% battery acid straight from the bottle into the reservoir without pre-mixing it in water.



Mineral acids - that’s hard core old school right there! :+1: :sunglasses:



Good idea for a thread. I’ve been using sulfuric acid for a couple years now and it works great. I figured it would add some more sulfur which should help enhance the smell, although I’ve never done a side by side with phosphoric acid.

I know on othe forums they bash the idea and insist people should use citric acid. But with my well water citric acid was almost worthless. It would lower the ph but within 24 hrs it had returned to near starting ph.


Battery acid was always the way to go, once and done. Just don’t mess with it when too stoned :laughing: :rofl: :call_me_hand:

I’ve been using citric acid (Real Lemon actually :stuck_out_tongue_winking_eye:) and yes, it drifts around - until the buffer in the tap water is depleated.

My excuse is… I had it… and its cheap at Costco… but yes, I have to check twice and sometimes re-dose and check again. You are correct, it’s a dog to work with.
I also had issues with what the local hydro store though pH Down was worth as well…

I find it hard to imagine anyone logically arguing against using sulfuric acid in favor of citric.



Citric acid does not provide any significant levels of elements, and the PH drifts quickly, and as a result you will find yourself using much more of it than you would with a sulfuric acid-based solution. Sulfuric acid is also the cheapest acid to use for PH lowering, and it is more stable with less PH drift, and the choice of most commercial growers


You are right, I need to ‘up my game’ and do it properly :+1: :sunglasses:
Time to look for some acid…



I found this the other day. I like the sulfuric acid it was cheap and easy to mix. I’m using up the last of my citric and phosphoric acids.


:wave: Always good to have this, but can we edit out the drink part? some people might be lysdexic or whatever & then we’d all have to deal with indigestion. :astonished: :alembic: :test_tube: :dizzy_face:

like keep baking soda around & stuff :sweat_smile:



good point - done. it was meant for humor but some people are clueless in that regard.


Oh I wasn’t trying to say citric acid is completely useless, it’s just not that great as a ph down. Maybe if working with RO water it can be effective.

I also wonder what amounts they would suggest be used as a supplement. I’ve seen it several times where it’s a root exudate and adding some could be beneficial but I’ve never seen a suggested amount. I’m also certain the amount need to adjust PH would be way more than would actually be needed


Ya I know you weren’t lol. I’d just seen that and hadn’t ever heard of it being used for that.

I’m using 1/4 tsp to 5 gallons to drop it from 8 down to 6.


To PH down I use either apple cider vinegar or LABs. The LABs has a PH of around 4 so you only need a tiny amount in 5 gals of water plus it boosts the soil bacteria.


lemon juice and vinegar both work to lower PH, however it is unstable and harder to keep it at a consistent range, so in the long run it will be more work, and will cost you more due to having to use more buffering solution, but whatever works for you is great.

Humic acid also acts as a PH down, and it benefits your plants.


I have humic acid in powder but it’s hydrophobic, and just floats around on the surface of the water.

The vinegar will keep the ph down for about 18 hours then it starts to climb again, and after a couple of days is back up around 7.5 to 8.

There is nowhere I know that sells sulphuric acid around here, I wish they did, I have several batteries I could bring back to life.


Yes, Humic acid is generally insoluble at any PH, however there is a nifty product called Black Earth DS-80 (DS stands for Dry Soluble) which is a soluble form of humic and fulvic acid, as well as added nutrients N and K. It is made by a company called Black Earth Humic, and is generally sold to large-scale farmers only, however you can find stores here and there that do carry it. There is also a product on Amazon called “Wow Soluble DS-80 Humic and Fulvic Acid Organic Fertilizer”, but I have never tried it, but it looks like it might be good and very similar.

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Thanks for the info I will look into that, Cheers.

Fulvex is a humic/fulvic acid solution. I have used it along with cider vinegar to lower pH. I am guessing that the issue is pH drift in a reservoir?

yes, in a res or in a cloner the ph can drift dramatically depending on the buffering agent you use. Fulvex and apple cider vinegar do work, however the sulfuric acid is much cheaper and more stable so it’s less work and less cost to maintain. Also, as mentioned, the sulfuric acid provides added goodness that other fertilizer or watering programs don’t, and the apple cider vinegar doesn’t really add any trace elements that are needed by the plants, as far as I am aware. But, to each their own - whatever works for you is great.


well…in soil drift is not an issue. In containers it is a good idea to pH. Sulfuric acid is much more caustic than household vinegar. And it were cheap I’d likely go white vinegar. Then some make an organic supplement with crushed eggshells and brown rice vinegar.

But as you say-


Growing media pH can also drift up or down depending on the balance of many different things such as acidification of the medium by the plant roots, lime activity and use of an acid or basic reaction fertilizer. Contrary to popular belief, the PH of the water does not influence the pH of the growing medium - it is the bicarbonate and carbonate levels in the water (known collectively as alkalinity) as well as the buffer you use to correct it, the potential acidity or basicity of the fertilizer and the plant itself.