PH Down: Citric Vs. Hydrochloric

Treeth said:

Ok, I got the down part-
But I do have to go up sometimes as well.

So I'm wondering if anyone knows a base that is as easily accessible and convenient as battery acid is.

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Ammonium hydroxide or potassium hydroxide. You can buy the former as household ammonia cleaner, and the latter off ebay - its used for biodiesel. I doubt itd make too much difference which you use, but for what its worth, ammonium hydroxide will increase nitrogen levels, and potassium hydroxide will increase potassium.

I just had an idea, maybe I could write a guide about pH? Here's a draft, lemme know if you can think of any improvements:




Getting the pH of your growing medium right is essential for the health of your plants. If the pH is wrong, it can damage the plant and prevent the uptake of nescassary minerals and nutrients. This is a guide to everything you never wanted to know about pH

As you'll probably remember from school, pH is a measure of acidity and alkalinity. pH'es greater than 7 are alkaline and pH'es below 7 are acidic. You ideally want a slightly acidic growing medium, with a pH of about 5 to 6.


Testing pH

First things first, you'll probably want to test the pH of your growing medium. Here are a few ways of doing that:

• Litmus paper - an old classic. This will tell you if your medium is acidic or alkaline. Thing is, it doesn't tell you how acidic or alkaline, so its fairly useless. Red indicates that it is acidic, and blue that it's alkaline. If you have to use litmus, you want it to show somewhere in the middle - a sort of purplish colour. I don't recommend it though, because of its lack of precision.
• Phenolphthalein (say phee-noll-phall-in) - as with litmus, this will only show you acidic or alkaline; so again, its very imprecise. If it stays colourless, that shows you that the medium's acidic, so you're on the right side of pH 8. If it turns pink, that means its alkaline and something's wrong.
• Universal indicator - this is better than the previous two. It often comes as strips. It gives you a more precise indication of the pH of the medium, but it can be a bit vague in the sort of reigon we'd be working in. pH 5-9 on universal indicator are all just different shades of green. This might be worth a try though.
• Phenol red - this is readily available as chlorine test tablets for swimming pools. It's a bit like litmus paper or phenolphthalein in the sense that it only tells you which side of a certain pH value the medium is, but it's got one thing going for it. It's red above pH8, which your growing medium will probably be in the first place (they have a tendency to turn alkaline). but then it changes through various shades of orange to eventually arrive at yellow at a pH of about 6. And remember what I said earlier? We need a pH of about 6, so if you just lower the pH till it stays yellow, you can't go too far wrong
• Electronic pH meter/probe - this is probably the best option. You can pick them up for a couple of quid off ebay and theyll tell you the pH on a screen. No messing about with identifying colours or whatever. Just a readout on a screen. Nothing could be simpler. Overall, this is the method I'd recommend.

Lowering pH

The chances are that your medium's pH will be too high (too alkaline). Not to worry, there are a few things you can add to lower it, just add these slowly (allowing them to dissolve and disperse) until the pH is correct:

• Vinegar - it contains acetic acid. I don't recommend this though, because it'll slowly evaporate and get broken down by the plants, driving pH back up
• Citric acid - another one you can find around the house or at the chemists. But again, it'll get broken down by the plants, causing the pH to fluctuate. Also, people get suspicious if you buy a lot of it here in the UK - its a monitored by the government because its used for clandestine spoon cleaning (don't complain to me, I didnt make the laws)
• Battery acid - this is a good one. It contains about 40% sulfuric acid, which also conveiniently supplies your plants with some of the sulfur which they need to grow. Contrary to popular beleif, sulfuric acid is NOT a bubbling green liquid which will burn straight through your hand instantly, and nor will it harm your plants when used in the correct amounts. I'd still recommend caution though: it is corrosive and it'll sting a lot if you get it on you. You have to buy it new though. If you pour it out of a used car battery, it'll contain toxic lead.
• Phosphoric acid - You can buy this as commercial hydroponics pH-down formula. It also contains phosphorus, which is useful when your plants are budding.
• Nitric acid - As above, it's available as commercial pH-down formula. Also contains nitrogen, useful during the vegetative period.

Increasing pH

No introduction paragraph here, just a list:

• Potassium hydroxide - available off ebay etc, because its used for biodiesel production. Make sure your store this in an airtight container at all times, otherwise it'll absorb moisture from the air and turn into a corrosive sludge. Contains potassium, useful for budding.
• Ammonia - you can buy solutions of ammonia as a cleaner at the hardware store. Alternatively, boiling a solution of urea (a high nitrogen fertiliser) will make ammonia. Contains nitrogen, useful during vegetative growth.
• Ammonium carbonate - you can buy this as baking soda. Make sure the baking soda is actually ammonium carbonate though, and not sodium bicarbonate. As above, contains yummy nitrogen.

Cool, thanks.

i find that this information is very informative mr(s) yournamehere.

wow i looked for this kind of great info 1 month ago and could not find this and it is written at the time i basically was searching. wow! this is very informative and i needed this. right now my pH is at 7.1, and i am waiting on an overwatering to cycle thru. and then i am going to do a flush using the battery acid technique. i have been using molasses and the pH is way up and also me thinks i have a lot of solids in my well water; it will flux from 7.0 -7.2. molasses will bring it up to 7.2-7.3 when the water is at 7.0.
I am starting flower (day 4). so a flush will be good i suppose.
I am using MG Organic Garden Soil, Perlite, a little sand, bone meal.
i really want these plants to settle down on all these changes now in flowering. one last transplant into 5 gallon buckets once sex is determined and that's it. I have learned a lot here at RIU and am grateful.
I have done everything that a person can do to ruin a grow.
Thanks to SuperThrive and most of all, RUI, i may have some more females from this stressful grow. as a matter of fact 3 are confirmed..
most of my problems were over watering and pH and i tried to find diagnosis in a nutrition thing. i looked nearly everywhere for nutrition fail and it was over watering most of the time.

Bla sa, bla sa, bla. IMHO No one should even consider growing hydroponically or aeroponically without the ability to daily, at a minimum, check their nutrient water 's pH. Given the amount of testing needed a pH meter is pretty much the only economical solution and the only solution that is simple enough that the pH readings are actually performed regularly. A conductivity monitor is also pretty much essentail unless you use a RO filter and change your nutrients entirely once or twice per week.

With a small amount of effort a good used laboratory grade pH meter by Thermo Orion, Oakton, Hach or YSI can be bought for $55 to $100. A laboratory conductivity meter with some patience and effort can be bought on ebBay for about $75 to $200 used if it is a Thermo Orion, Hach, Oakton or YSI.


For pH down Phosphoric Acid and/or Nitric acid are the best choice and are used in the more expensive pH down solutions such as Dyna-grow. They are also the acids typically used by prodfessional horticulturlaists for aeroponic nutrient solutions, some however do cheap out and use sulfuric acid, but this should only be done for a formualtion designed for your water and needs so as to prevent having to much sulphur in your nutrient solution. Phosphorous and nitrogen provided Phosphoric Acid and/or Nitric acid are heavily used major nutrients so using them as a pH down will not cause over abundances as can happen with sulphuric acid. "Even when budding." Non mineral acids such as vinegar and citric acid should be used only for emergencies when nothing else is available because they often cause a blooming of bacterial growth in the nutrient water which lowers levels of dissolved oxygen which reeks havoc on the roots and inturn o loewers the pH as the levels of CO2 increase and carbonic acid is formed.

Potassium Hydroxide is a good pH up as the Pottasium is also a major Nutrient. A bit better pH up is a combination of Potassium Hydroxide and Potassium Carbonate as the hydroxide raises the pH and the carbonate buffers the pH. Once again the more expensive pH up by Dyna-grow uses this better combination.

Either pH up or pH down are easy to formulate and mix, but that would be in a different thread.

what are the over abundances caused by sulphuric acid?
i will use blooming solution that has a little nitrogen in it.
medium is a compost mix.

rural hick said:

what are the over abundances caused by sulphuric acid?
i will use blooming solution that has a little nitrogen in it.
medium is a compost mix.

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Sulphur (sulfates). Sulfur is only a minor nutrient not a major nutrient. The other choices as a side effect supply major nutrients. Although sulfate is used at higher levels than the micro nutrients it is still usually more than adequately supplied by the magnesium sulfate used to provide magnesium in liquid nutrient solutions.

Many nutrient manfacturers use no sulphur in there formulations or only levels nearing those of micronutrients.


The only deficiency sign of a sulphur deficiency is a yellowing of upper leaves. It is usually more commonly a problem during budding as all chemicals that are related to alkalinity carbonates at re often problems during budding. Usually this is rectified by adding magnesium sulfate during budding (and Iron and phosphate). It is not common to have a need to lower a nutrients pH during budding. and suing it to lower the pH of the initail dudding nutrient will cause a high sulfate level once you raise thr magnesium level with magnesium sulfate. Magnesium deficiency causes early yellowing of lower leaves, red stems, Necrosis, and white leaf tips. Looks alot like the results of flushing a plant before harvest but it happens before the flush or it makes the final flush cause severe signs of nutrient deficiencies.

Muffy D said:

Has anyone noticed a difference between the two?

"When I ran out I got the citric acid kind from home depot and it lasted 3 days. My res got all cloudy and the ph levels would keep going up."

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I almost gave up on hydroponics because of citric acid.

I had thought there was some sort of bacteria in my nutrient solution because every day my ph would spike up to over 8. A day or so after each nutrient change, my water would go from clear magenta to brown, muddy, and slightly foamy. I couldn't figure it out.

Then, after endless web searches, I found that my problem was citric acid. It breaks down very quickly, you see, so its ph lowering ability goes away after a day or so. Its by-products make the water brown and cloudy. Don't use citric acid.

I switched to sulfuric acid, and my problems went away that very day. My nutrient solution stays clear, no brown, no foam.

I know this is an old post, but I'm replying to help anyone who is inexperienced enough to try citric acid in hydroponics.