Alrighty, let's review...
Good tea is like a fire (work with me here
) Like the fire it has three main needs, what firefighters learn as the fire triangle.
Fuel (food), temperature, and air are the key elements in fire building or tea brewing. The first two are easy for tea; we add our fish and kelp and such and we have fuel, and when we are making tea getting above 50 degrees is pretty much a given. So air is our key concern here.
Our air is doing two things in brewing; adding oxygen to the mix by increasing surface area, and even more importantly, circulating the brew. While the former seems ostensibly more important, the gas exchange is still primarily taking place at the surface of the brew. So moving bottom to top is our prime concern really.
Let's keep in mind that small, cheap aquarium units are for moving crystal clear water, hardly the viscosity we are attaining in our teas. I would prefer something a little hardier to keep up the flow; as biology builds in the stones the flow will be decreased enough already, so no point in skimping on the cheap stuff to get lacklustre results.
So avoid tiny little stones and cheap air pumps. I am not a fan of those blue composite stones; they break down and clog really quickly. The glass bead or ceramic types clean up better but are a bit more expensive. I think if I was building a tea brewer today I would go with the[url=https://www.thepondreport.com/disc-diffusers.shtml]new diffusers[/url]. A very fine bubble and a mass of them to keep circulation moving. While we debated bubble size in the original AACT thread, it was more about clogging a fine stone than anything and these new diffusers clean up nice. Get two or more and swich them out between batches; as Dr. Ingham always used to tell us, "Dessication is the best sterilant".
As for pumps, the gold standard is the [url=https://www.aquacave.com/s31-sweetwaterbr-regenerativebr-blower-12hp-2030.html]Sweetwater[/url]; this is what they use in the big aquariums, but it isn't out of reach (and this is the one they used in the Dirt Simple brewer that Dr. Ingham helped develop). But I think you can do cheaper and still do well. [url=https://www.aquacave.com/detail.aspx?ID=2799]This one[/url]caught my eye; moves a good deal of air and you can adjust
(how cool is that?) to fit your container, your stone size, how thick the tea is, if the stone is clogging, etc. Cool.
So avoid cheap, buy right and you will be happier longer and make better tea. My grandpa always said "Buy the best and you will always be happy with your purchase." I don't think you need to go that far in this case but the cheap stuff will definitely make you unhappy in the long run...
Hope that helps