Filter Wool

Any filter wool will do the job. A roll of it works out cheaper. Just use a Juwel one as a template to cut it up.

The filter wool in the Juwel filter is unusual being first in the direction of water flow. Most filters have it last, to polish the water (ie remove the tiniest particles). Juwel have it first to trap debris to stop it getting further into the filter. This means it gets clogged very quickly and it falls apart after a couple of washes. Changing it every few weeks works out expensive if you use Juwel replacements. And changing it frequently means that there won't be many bacteria on it so you remove a tiny proportion of the total bacteria. They don't grow very well on filter wool anyway.

I agree with biffster on this. I have one of these tanks and I've given up bothering with the filter wool. There is room for 6 pieces of media in the filter, more than you get with most filters for tanks of this size and enough for plenty of bacteria. Taking out the wool means that the flow rate doesn't slow down as quickly.