This is the original way the holding tank filter comes except I already cut the label to start this project. These filters cost between $60 to $85 depending on where you can buy them. After this refill modification which cost about $10, a yearly refill only cost about $4 for the carbon.
I found a bunch of the pellet carbon on-line for $8 and that would last me 2 years. (Actually, I now have enough for 8 years.........) If an average of $70 each per year, over 8 years would be $560. This whole thing cost me less than $40, so I'm over $500 ahead I think!
This refill modification is not my original idea. But I did modify it for my application and did what I feel are some improvements.
Don't forget to click on the pictures for a larger view.
I cut the original filter on one of the sides. That way it makes it easier to fill up with the new carbon pellets. Rather than cut it in the middle and trying to put the 2 halfs together full of pellets.