Oxygen levels rarely get the attention they deserve in an aquaponics setup, yet they can make or break your system. Below you’ll find the reasoning behind adding an air pump to your setup, plus practical guidance on picking the right pump and air stones for your situation.

Why does an aquaponics system need an air pump?

An air pump’s job is to keep oxygen flowing to both your fish and the roots of your plants. Skimp on aeration and you risk several problems at once: fish gasping from low oxygen, roots rotting in the growbeds, and die-off among the beneficial bacteria that handle nitrification.

Several things in your system are constantly pulling oxygen out of the water:

• Fish
• Plants
• Bacteria
• Algae

Pairing an air pump with air stones also gives you a safety net – if your main water pump ever quits, the aeration setup keeps your fish breathing. It’s an inexpensive form of insurance that lets you sleep easier.

Low-oxygen water is also where many disease-causing organisms do best, so raising your dissolved oxygen level helps keep those pathogens in check.

Warmer water holds less dissolved oxygen, which is exactly why fish losses spike most often in the hottest months. The more oxygen available in the water, the less effort a fish has to spend extracting it. As a rough guide, tilapia and catfish get by on roughly 2-3 mg/L, while trout need closer to 8 mg/L. There’s no downside to running levels a bit higher than these minimums – in fact, extra dissolved oxygen is welcome. Keeping algae growth under control matters too, since algae competes with your fish and plants for oxygen. On top of all that, aeration helps release harmful gases produced during denitrification.

How does aeration actually work in an aquaponics system?

You can aerate a system two main ways:

• Letting the flow of water disturb the surface
• Using an aerator (air stones) to disturb the surface

Either method raises dissolved oxygen by agitating the water and breaking up the surface tension in the fish tank – whether that agitation comes from moving water or from bubbles rising off an air stone.

Where should air stones go?

Growbeds

A flood-and-drain growbed already gets its oxygen from the draining cycle itself, delivering air to both the roots and the bacteria living there – so you don’t need air stones in the growbed. Your fish tank, on the other hand, does need them.

Deep water culture (DWC)

Because the roots in a DWC channel sit fully underwater all the time, this setup demands more oxygen than a growbed does. If you’re running a biofilter, give it a few air stones too, and make sure the fish tank has one or more as well. Overall, DWC is the thirstiest setup for air supply.

Nutrient film technique (NFT)

NFT doesn’t need nearly as much air as DWC. Here, aeration is typically limited to the fish tank and the biofilter.

Deep flow technique (DFT)

A DFT setup calls for air stones placed in the channels themselves, or just ahead of them. Unlike NFT, which relies on a thin film of water in the gutters, DFT runs an inch or more of standing water through its channels.

Mineralization tank

If your system includes a mineralization tank, drop a few air stones in there. This feeds oxygen to the solids-digesting bacteria and helps keep the solids circulating. If you’re not running growbeds, adding a mineralization tank is worth doing.

How air actually diffuses into the water

Dissolved oxygen enters the water column through diffusion, and air stones are what make that happen. Generally speaking, smaller bubbles diffuse oxygen more effectively – but producing smaller bubbles asks more of your pump in terms of pressure. Bubble size is also shaped by how fine the pores are in the air stone itself.

Placing an air stone deeper means your pump has to work harder, since it’s pushing against more water pressure. You might assume setting the stone just below the surface would be easier and just as effective, but that’s not quite right – diffusion also depends on how long each bubble stays in contact with the water on its way up. Depth also influences how much of the water column gets circulated.

Choosing an air pump for your aquaponics system

There’s really no such thing as too much aeration capacity in aquaponics. I haven’t come across a rigorously tested formula for sizing an air pump specifically for aquaponics, since too many variables are involved. There are, however, published formulas for calculating oxygen requirements in general aquaculture settings that you can look up for reference if you want to dig deeper into the math.

Choosing air stones to match your pump

Once you’ve picked a pump, check its flow rating, usually given in liters per hour or per minute. For example, say you have a 60 liter-per-minute pump fitted with a manifold and valves so you can split the output. If you run 5 air stones off that manifold, each one would handle roughly 12 liters per minute. In that case, you’d want to choose air stones rated for around 10 liters per minute of flow.

Sample air pump setups for aquaponics

Growbed setup – roughly $39 total:

• Hydrofarm Active Aqua pump, 6W, 15 L/min
• Pawfly air stones, 2 L/min
• 25 ft of air tubing

Small DWC setup – roughly $88 total:

• Vivosun pump, 32W, 60 L/min
• Five 4-inch air stones
• 25 ft of air tubing

A couple of tips: Keep all your air lines the same length and set every air stone at the same depth – air naturally takes the path of least resistance, so uneven lines or depths will starve some stones of airflow while others get too much. Also, mount the pump above the water line unless you’ve installed one-way check valves; without them, a power outage can let water siphon backward through the tubing and flood the pump.

Common air pump problems

The pump keeps overheating

This usually happens when the pump can’t push out all the air it’s generating, so pressure builds up inside it. Adding an extra air stone to one of the open outlets gives that pressure somewhere to go. You could also fit a bleed valve that vents excess air to the atmosphere, though that just wastes air – adding another air stone is the better fix.

What does it cost to run an air pump?

Here’s a sample calculation using a 32-watt pump running continuously, with electricity priced at $0.12 per kWh:

• 32 watts x 24 hours = 768 Wh per day
• 768 / 1000 = 0.768 kWh per day
• 0.768 x $0.12 = about $0.092 per day
• $0.092 x 365 days = about $33.60 per year

How can I make the pump quieter?

Most pumps ship with rubber feet that absorb vibration and cut down noise. You can also add a diffuser or dampener to the compressor’s air inlet for further noise reduction.

My air stones keep clogging

Over time, algae and solid debris will build up inside an air stone and reduce its output. Scrubbing it periodically with a toothbrush is usually enough to restore good bubble diffusion. If you’d rather skip air stones altogether, a venturi is a workable DIY alternative worth researching.