So I have to install a charcoal air filter. There are plenty of online tutorials about them so it's not hard to make.
However one thing about charcoal air filters is that they work based on surface area. You need a lot of small pellet size pieces that are washed to remove dust and then put in a medium where the air passes thru.
The interior of the charcoal gets little air contact so it is basically the surface of the pellets that do the work.
This got me to thinking about a different type of charcoal filter.
What if the charcoal was sponge like? Like open cell foam used in auto air cleaners or the inside of my shop vac filter?
Well turns out, it is easy to make this type of charcoal. In fact it's so simple and stupid. I don't know why it is not done now.
The secret ingredient is bread.
If you put bread into a glass cooking vessel like a casserole dish, and with a lid on it, then proceed to leave it in a very hot oven until it is black, you just made spongy charcoal.
Very gently take the spongy charcoal, cut it with a saw and make a custom fit pieces for your aquarium filter or even to breathe thru.