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I've decided to try out active aerated compost tea but I'm unsure of how much aeration to provide, and how. I've seen that I should target 5.5+ ppm oxygen in the liquid, but I have absolutely no sense of how quickly oxygen will be consumed or what putting it back in the tea would look like.

Some online guides show 5 gallons of tea aerated by a 1-gallon-per-minute aquarium air stone, and others pump tens of gallons of air per minute for the same amount of tea. Sometimes they pump the air through an air stone, sometimes through something more sophisticated. I see that the size of the bubbles has a big impact how effectively they oxygenate the water, so it's more than knowing what volume of air to pump through for a given amount of tea.

So my question is, for a given amount of compost tea, how do I aerate it adequately and economically?

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    Why not skip the entire tea bit and just use the compost under your mulch? As far as I know, there is no scientific evidence that aerated compost tea actually does anything positive for your plants, and there is evidence that it actually can harm the plants as far as foliar diseases go. If you know of any scientific studies that actually show helpful effects from this tea, please add a citation to your question.
    – Jurp
    Jun 9, 2023 at 23:01
  • @Jurp This question is about creating compost tea, I think it would be better to ask after the efficacy in a separate question.
    – MackM
    Jun 10, 2023 at 2:08
  • My point is, why bother with making the tea at all if there's no scientific evidence that it even works?
    – Jurp
    Jun 10, 2023 at 11:37
  • @Jurp I understand. It's because I want to try it out.
    – MackM
    Jun 10, 2023 at 13:28

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Fish stuff will be the most economical method for any reasonable home scale, or you can go to pond fish stuff for unreasonable home scale.

You can pump air into the bottom, using an airstone or bubble wand, or you can pump water (tea) up and let it fall back into the container. Both will keep the fluid circulating, which means it will come into contact with the air at the surface as well as any bubbles involved - so the air exchange is not entirely dependent on the bubbles. If and only if you have trouble with the airstone/bubblewand clogging, you could remove it and use an open air tube.

Unless you invest a rather large amount of money into an oxygen meter which probably won't much like (and therefore may expensively expire from use in) tea, just choose an air or water pump as if it was an aquarium of the volume of your tea, and it will likely be fine. There's probably very little if any practical benefit to massively overscaling the amount of air pumped, but extremism sells on youtube.

Pumping air into the tea will be less affected by particles of compost than pumping the liquid will be.

If you want to delve into the science of biochemical oxygen demand in aqueous solutions, there's a massive amount of data from wastewater treatment - but applying that to a 5 gallon bucket is generally impractical.

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  • Could you please point me to some of those wastewater treatment references on oxygen usage? I have not been able to find any information on how quickly I can expect the oxygen to be consumed, just how to put more in. I'm hesitant to approximate based on aquarium equipment because I suspect the tea would consume oxygen much more quickly than a healthy aquarium.
    – MackM
    Jun 10, 2023 at 13:45
  • I just ran a rough calculation using some of the figures from those links and came up with about 4 gallons of air through a fine diffuser in a 5 gallon bucket (assumed depth 1 foot) to put it at 5.5ppm in one minute, starting from zero. Which would be a VERY high BOD indeed. So I'm quite sure 10 gpm air would be massive overkill and 1 gpm air is still overkill. I'd estimate 1 liter per minute as utterly fine for 5 gallons.
    – Ecnerwal
    Jun 10, 2023 at 20:41

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