The Best Air Pumps For Hydroponics

oxygen depletion in hydroponics

Without oxygen in their environment and surrounded by water, plants will go through the same drowning processes biochemically just like mammalian organisms. Hydroponics needs water to dissolve nutrients for them to become available to the plants for growth and thus there’s a constant compromise between optimal nutrients and optimal oxygen.

If your reservoir doesn’t have a lot of oxygen but an adequate amount for your plants to survive, the conditions may be anaerobic enough for bacterial or fungal colonies to build up. If this happens you’re going to suffer from a plague of root rot which certainly will kill your plants. Symptoms of root rot include brown, slimy roots which smell like decay, if you believe this may already have happened then take a look at how to cure root rot here.

Simplistically, air pumps transfer air from the external environment and into the reservoir containing your nutrient solution. The bubbles produced are in contact with the nutrient solution and oxygen is dissolved into it. The smaller the bubbles, the higher the surface area and the more oxygen can dissolve through to be available for absorption by your plant’s root zone.

The maximum amount of dissolved oxygen in water is termed the saturation value, and measurements are either as a percentage of the total saturation value or in mg/l. The temperature of the nutrient solution in your reservoir affects the saturation value. The cooler the water, the more oxygen can be dissolved in it.

Approximate Dissolved Oxygen Saturation Values (At a salinity of 30ppt):

Temperature(℃)	Dissolved Oxygen (mg/l)
30	6.4
25	7.0
20	7.6
15	8.4
10	9.3
5	10.5

[source]

what size of air pump?

The size of your air pump is dependent upon the size of your reservoir. The more water it holds the more oxygen must be dissolved into it so getting the correct size of air pump is essential for plant health.

Each air pump will come with a set of specifications, including the wattage it uses. One watt for each gallon (3.7L) will be more than adequate for your setup. Another specification to look out for is whether the pump can move 500-600 cubic centimetres of air per minute. This should be fairly straightforward for modern pumps and amatuer growers will be catered for. The more power a pump has, the more it works and the more it works, the louder it becomes.

Noise Pollution

If the system is located in an area of your home which you spend a lot of your leisure time in, take the noise into consideration. You will want to look for a pump with a decibel level of below approximately 45 decibels.

It’s the vibration of the device which makes the noise. To minimise the vibration-induced noise, remove the surfaces coming into contact with the pump. If it’s possible with the model you choose, attach a paperclip to it and slide a rubber band into the paperclip to then hang off of something. You could also glue felt feet to the bottom of the pump so it sits slightly raised relative to the surface it’s placed on.

What else do you need?

It’s all well and good owning a pump but to get the oxygen into the nutrient solution you also need some airline tubing and an airstone to disperse the bubbles as finely as possible to increase their surface area. The tubing must be dark in colour to avoid any unnecessary algal growth build up inside the tubing from light penetration.

Airstones will produce different sized bubbles which, as we stated before, will affect the rate of oxygen diffusion into the nutrient solution. Halving the size of the bubbles will approximately double the surface area in contact with the water. Smaller bubbles won’t rise to the surface as quickly as large bubbles either, increasing the time of diffusion too.