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.

3/5 trays in my canister filter are media.

Ceramic/Stone type media is so much better than plastic balls or anything plastic.