The term pH Down refers to commercial products or regular household substances that are added to a hydroponic nutrient solution in order to bring down the solution's pH levels, helping in become more acidic. The term is often in the title of commercially available products, or household products can be used instead.
Commercial pH Down products generally contain food-grade phosphoric acid. Household products like lemon juice can also be used to lower a hydroponic garden's pH levels.
In contrast to pH Down products on the market, there are also pH Up products available. Such products typically contain potassium hydroxide and potassium carbonate; otherwise regular baking soda can be used in a pinch.
Explain pH Down
In hydroponics, the pH level of a nutrient solution is a good indicator of how strong the solution is. It needs to constantly be monitored to ensure optimal plant growth. Measuring the solution's pH levels allows a grower to see if their nutrients/plants are either too acidic or not acidic enough (alkaline).
Upon determining that their nutrient solution's pH is too high (too basic, or alkaline), a grower can make quick adjustments by using pH Down products, which usually contain food-grade phosphoric acid. Balancing pH levels takes practice and some trial and error. It is advisable that a grower adds only a little bit of pH Down product at a time if the nutrient solution's pH is too high in order to lower the pH to the proper level. While store-bought solutions are recommended, growers can use things like lemon juice as a pH Down solution.
Because pH values fluctuate easily with minimal input, it is advisable to start off with very small amounts of pH Down and continue testing the solution with a pH pen, pH meter, or litmus paper until the ideal pH value is reached. In hydroponics, the ideal pH for most crops falls between 5.5 and 6.5, which is considered to be slightly acidic. It is considered easier to raise pH levels using pH Up products than it is to lower them with pH Down products. Most growers have both products on hand.
Many things can affect the garden's pH values, including nutrient levels, water quality, algae growth, and the choice of grow medium. Also, pH values change over time as plants grow and uptake more and more nutrients.
pH values also apply to soil gardens, but the terms pH Up and pH Down are generally more so used in hydroponics than traditional gardening methods. For example, while horticultural lime or limestone is a popular soil amendment primarily used to increase the pH of a soil or lawn, it's not often referred to as a 'pH Up' product.