PH is a way of measuring the acidity or alkalinity of a substance. The scale for pH readings ranges from 1 to 14. Unadulterated water registers a completely neutral reading of seven. A reading of seven means that the number of acid ions is totally equal to the number alkaline ions present in the measured solution. Any reading above seven indicates that alkaline ions are in greater number, and any reading below seven indicates that there are more acid ions. Each number above or below seven indicates a tenfold increase in either acidity or alkalinity. So a substance with a pH reading of five would be ten times more acidic than a substance with a reading of six. This is important to remember for hydroponic growing, because even if the difference seems slight between your ideal pH and your actual pH, the difference may actually be a huge problem.

The optimal pH for a nutrient solution is 5.6. If you are growing in soil, it should still be slightly acidic, but closer to neutral at 6.3. If your nutrient solution or growing medium is too acidic or alkaline, many of the vital nutrients will be precipitated into certain useless salts, which means they will not be absorbed by the plant. For example, a solution that is too acidic would create a deficiency in calcium. This would probably damage your root system, causing the roots to rot and fall off and making your leaves wilt and develop "dead spots." On the other hand, if the solution is too alkaline, your plants will not be able to absorb iron. This can cause chlorosis, a disease that makes plants produce insufficient chlorophyll. This would then mean that it could not produce adequate carbohydrates through photosynthesis and it may die if the deficiency becomes too severe.

The pH of the water you intend to use for your hydroponic growing should be determined before any of the nutrients are mixed into it. Nitrazine paper is inexpensive and readily available can be used to quickly test the pH level. You may also use the pH kit from your swimming pool to test the pH. If you really crave accuracy in your pH tests, you can purchase more advanced testing systems from most gardening supply stores.

Among the most easily obtained ingredients that can be used to lower a high pH is aspirin. Another popular and cheap method is using small amounts of distilled white vinegar.

A low pH can be corrected by adding either potassium hydroxide or sodium hydroxide to the water. Only very small amounts of one or the other should be needed. Because the hydroxides are dangerous, they should be used very cautiously. Never touch hydroxides when your hands are wet. In fact, you should do what you can to handle them as little as possible and use sturdy rubber gloves when handling.

The main problem with cheaper methods is that they are not precise and may affect your plants adversely. You are much better off purchasing a pharmaceutical grade pH adjuster built specifically for hydroponic growing. That way you have a better chance of accurately adjusting your pH for optimal growing conditions.

Always test how your pH adjustments on one small plant before you continue to make adjustments to your entire nutrient solution. This will ensure success both in the present and the future. Good luck!