Chicfarm: www.chicfarm.org: The science of dissolved oxygen (DO) in a Non-circulating hydroponics method

1. All plant roots must have oxygen. In a hydroponic environment it is essential to ensure your plant’s roots are supplied with oxygen. Growers must be well versed in the science of dissolved oxygen (called DO).

2. Most crops seem to prefer about 9 PPM DO, some crops like lettuce have demonstrated little to no difference in fresh weight or dry weight when grown in DO levels ranging from 2.1 PPM to 16.8 PPM (Albright et al, 1996). So lettuce is the best crop to grow in hydroponics.

3. Dissolved oxygen levels in tap water are typically between 5-7 parts per million (PPM) at room temperature. Temperature has a powerful effect on how much oxygen can be held by water molecules. The warmer the water is, the less gas it is able to hold. Fully oxygenated water at 68° F will hold about 9 PPM of DO, while the same water at 86° F only holds about 7.5 PPM (over 15% less DO). It should come as no surprise then that the ideal temperature for maximizing root growth in hydroponic systems is 68° Fahrenheit, the temperature at which water naturally holds the 8-9 PPM of DO, which is the very amount of DO necessary to support vigorous plant growth in most crops. Water holds both dissolved solids like fertilizer as well as dissolved gases like CO2 & O2. The higher the PPM (dissolved solids), the less gases water can hold, so be aware that over fertilizing often occurs in conjunction with oxygen eprivation.

4. There are 2 most cost-effective ways to increase DO in the water: grow air roots and pump air into water. First way is totally free. You just need to help plants to generate air roots as many as they can , so O2 will be delivered by leave to the air roots and transformed into DO in the solution.

5. The other way is to use Air Pumps & Air Stones
Air diffuses into water whenever water comes in contact with air. This commonly occurs when water on the surface of a reservoir touches the air in a grow room or when air bubbles rise through a column of water in a reservoir. Many growers employ the combination of an air pump and air stone to add oxygen to their solution (the mixture of water and nutrients). This is a viable option for many growers which is able to increase DO levels fairly inexpensively. An air pump pumps air through plastic tubing to the bottom of the reservoir, where it is attached to an air stone. The air stone then diffuses the air into small bubbles which rise through the water, increasing the DO level as they rise. This also happens to be a great method for keeping one’s water and nutrients mixed, preventing the nutrients from settling to the bottom of the reservoir.

The size of the bubble that an air stone produces makes a significant difference in their ability to add dissolved oxygen to water. If a single large bubble and 8 small bubbles have the same total amount of air inside of them, then the surface area of the smaller bubbles will always be greater. Additionally, smaller bubbles are less buoyant and rise through the water slower, allowing them to diffuse more oxygen into the water.