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adjusting pH in hydroponic systems

What are the disadvantages of using white vinegar to lower the pH in my hydroponic system?

I have read that I should use phosphoric acid. But I have also read that phosphoric acid could be bad for hydroponic systems with hard water. I am using well water with a starting pH just below 8.

I also heard that nitric acid would be good for hard water but that the acid may be too aggressive for most novice users.


Here is general information on growing hydroponically from Virginia Cooperative Extension:

Hydroponically grown plants must obtain all their nutrients, including trace elements, from the nutrient solution. Success or failure may depend on precise and complete fertilizing practices. Complete nutrient solutions, specifically made for hydroponics, take the guesswork and the mess out of mixing one’s own formulas. All hydroponic nutrient solutions must be changed after a short period since evaporation causes concentration of salts in the water. Adding fresh solution to old solution would only make things worse. During spring and summer, pour spent nutrient solution around trees and shrubs.

Here is information from on adjusting pH in your hydroponic solution:

* The pH value refers to the acidity or alkalinity of the nutrient solution.
* pH readings run from 0 to 14 (0-6 acidic; 7 neutral; 8-14 alkaline).
* The recommended pH level for a general hydroponic solution is between pH 6 and pH 6.5. (Nicholls, 63)
* Many different variables can effect the pH level.

o Temperature
o Amount of light
o Evaporation
o Tap water refining
o Amount of nutrients

* With this amount of variables, periodically checking the pH level of the solution is vital to maintain a healthy environment for the growth of the plant

* Adjusting the pH level of the nutrient solution can be done simply.

o If a solution is too acidic, add one tablespoon of baking soda to three gallons of solution.
o If a solution is too alkaline, add one tablespoon of white vinegar per four gallons of solution.

This link to Texas Agricultural Extension Service addresses growing vegetables hydroponically, and offers details about nutrient solutions:


The book, Home Hydroponics…and How to Do It by Lem Jones (Crown Publishers, 1990) suggests testing the salt content of your water. Since you are using well water, you would need to contact the State Water Board (here is a link to Department of Ecology’s Water Resources page).

If the total amount of dissolved salts in your water is less than 700 ppm, the water should present no problem. This same resource says that a pH of 5.8 to 6.2 should be good for most plants. Since your pH is alkaline, you will need to acidify the solution. For adjusting a few gallons of solution, two regular aspirin per gallon of water will lower a pH of 8.0 to near 6.0. You can use a teaspoon of white vinegar per gallon as an alternative method. In a large system, this book recommends using sulphuric acid, but protect yourself from acid splashes and always pour the acid into the water and not the water into the acid.

The book Hydroponics for the Home Gardener by Stewart Kenyon (Key Porter Books, 1992), confirms the above, but remarks that vinegar is only a temporary measure and its effects will not hold for more than a few days. The author recommends using phosphoric acid, which he says is nearly harmless–just be sure to wash any spills off yourself right away with baking soda and water. If you add 0.1 millilitres of phosphoric acid per one gallon of water with a pH of 8.0, and a hardness factor of 136 parts per million, the pH should be reduced to 6.8.