You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
Do you need a powerhead for a Biological filter
I've had good luck for my 20g with a single bag of seachem matrix and 1 and a half sponges all crammed into my hob.
I also have a small bag of seachem matrix stuffed into the cavity of a fake tree stump decoration
As stargirl says, depends on what filter you go for. Nitrifying bacteria lives on all surfaces in the tank, but decent porous biomedia provides a greater surface area so the bulk resides in the filter media. If you have a small filter (HOB, internal etc) then you are limited to how much you can have, whereas a canister can fit in a lot more. Most HOBs will allow you to fit in a decent sized bag of media which should be adequate.
Seachem Matrix is really good as media! There isn’t a maximum but try to use as much as physically can in your filter.