Compost Teas and Air Pumps

[Alex Veidel]

Hi y'all

Couple questions. I've been trying to play around with compost teas, but I think I'm just missing a piece of information about air pumps. In aquaponics, we usually categorize water pumps by gallons per hour. I've been trying to size air pumps for various size compost tea brewers, but I'm getting a little hung up on the terminology. What unit of measurement should I be relying on? Watts, liters per minute?

So, using whatever terminology is best, is there a decent rule of thumb (besides bigger is better) to get an idea for how big of an airpump to use for a certain size batch of compost tea? I'm sizing for a 5 gallon as right now.

Oh, and one more thing. I've already got a 60 watt air pump with 5/8 hose output. I keep hearing that too much churning can damage microbes, but I can never seem to find the numbers on how much is too much. Obviously I'll have to play around with it, but if some general parameters exist, I'd love to hear them :)

[Glenn]

Hey Alex, I've always been told that trout require 6.0 to 8.0 mg/L of dissolved oxygen. And  that catfish and tilapia minimum levels can be as low as 2.0 or 3.0 mg/L although the recommended levels are 5.0 to 6.0 mg/L. We also know that low oxygen can become deadly for all fish very quickly. And we know that our plants need oxygen to their roots and good air flow around them. And of course the bacteria all need oxygen in one way or another. SO I know through raising trout that 8.0 to 11 mg/L as a target works for my target. 11 gives enough time to get back-up oxygen equipment going in any power, or pump failure.

The problem I ran into when trying to size air pumps is that they are all different, the stones are different, and the recommendations by their distributors vary in size and standard measures. So, having set myself a target of 11 mg/L which translates also to 11 ppm. And knowing that I try to provide 5 to 10 gallons per adult trout weighing 1 to 2 pounds at harvest, I have learned that using a personal rule of thumb of 1 CFM (cubic foot per minute) to 100 gallons of over all water volume works best for me. (Not just fish tank volume but all of it).  So I guess that it could be ok for Tilapia if  that were halved. or a ratio of .5 cfm per 100 gallon of system volume. I personally don't advise that though because really less air won't save all that much and 1 to 100 is far from saturation nor does it require too much churning. Higher altitudes and higher temperatures requires higher air flow for the  same diffusion.

Normal water pump flow and cascading oxygenation methods should still also be included, but I use this ratio of 1 cfm/100 gallon of water to determine pump and diffuser sizes. I hope it helps you.

[Glenn]

I meant to add that instead of fish weight, I think this ratio translated to the weight of your bio tea material would be ideal. And after typing I checked calculations for altitude differences. I live near sea level and it looks like for every 1000 ft. above sea level, an additional 4% air volume should be diffused. or in the Denver area 1.2 cfm of air to 100 gallon of trout water and 1.2 cfm of air per 20 pounds of tea organisms.