Originally posted by TCLynx on AGC, May 31, 2010
Additional aeration is often a good idea in aquaponics. How that aeration is best provided is sometimes a hotly debated topic.
Anyway, here are some numbers to help choose an air pump if that is the method you choose.
1 cubic foot per minute of air will take care of 400 gallons of water. It takes about 1 psi to push the air through an air stone and another psi for every 28″ of water depth.
So if you have a fish tank with about 28″ deep water that is only 400 gallons, you want an air pump that can provide at least 1 CFM of air at 2 psi. Air pumps come with performance curves the same way water pumps do but it is volume at different pressure rather than height. So if you only have a 100 gallon stock tank for a fish tank, an air pump that will deliver .25 cfm at 2 psi will be enough. If your fish tank is deep, it will require more psi to push the air down to the bottom.
Large high quality air stones are worth a little extra since the cheap little ones usually fall apart or can’t be cleaned. I’ve had mine running for over a year now and not had to do anything special with them. I usually try to soak a new air stone in water for an hour or so before hooking it up to the air pump.
I’ve plumbed from the air pump to all my different fish tanks with regular water plumbing pressure pipe and then placed ball valves at each tank the use a nylon threaded to barb fitting of the correct size to hook up the tubing that goes down to the air stone in the bottom of the fish tank. One benefit of using air pumps for additional aeration and backup is you can use air from a single pump to support and backup multiple systems and tanks, you just need a big enough air pump for the job.
I do have my air pump hooked up to a battery for backup in case the power goes out since a heavily stocked fish tank can run out of dissolved oxygen pretty quickly if the system shuts down.
In many systems the regular pumping and water flowing back to the fish tank provides aeration but if the pump cycles on and off and the off cycles are too long, the fish could suffer from the lack of aeration. If pump cycles are going to be far apart, one should provide supplemental aeration to the fish tank in some form. I’ve also found that additional aeration can help keep the water circulating in tanks and help the solids move on through the system rather than settling in the fish tank. With ample aeration, fish eat better and grow faster. Bacteria also work better with well aerated water. In raft systems or constant flood systems, plants will grow better with excess aeration.
Now there are other methods to aerate water. Some people use small pumps to lift water and spray it back into the same tank. Trick there is finding an appropriate small pump that won’t clog up constantly. I have had difficulty finding a small pump that would provide enough aeration without clogging but I know some people have had good results this way.
I think a system using Nate’s towers directly over the fish tank probably gets enough aeration from the system aeration and I would simply hook such a system to a battery backup so it could keep running entirely on backup instead of only air running when on backup.
Raft systems need more aeration but I don’t have enough experience to know how best to provide the additional aeration for a raft system.