I used a coarse black filter medium, that I got at
www.watergarden.com, in my biofilter, a 50 gal Rubbermaid stock tank. The filter medium is 1 1/4" thick and 56" wide. It sells for $13.99/linear foot. I cut it into 2" squares with a razor knife and put into black polyester mesh bags. It works wonderfully. My ponds are crystal clear in the growing season.
Here is copy of the info on it from their website: (there is a photo of it on their website)
"Click to Enlarge
Fiber Filter Media (Black)
Qty. Add to Cart
Only $13.99 ea.
Item Number: FMM045
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Fiber Filter Media (Black)
1-1/4 inch Thick x 56 inch Wide cut to order (Black) Stiffer than the white media and longer lasting. (note: 56" width can vary, we have seen this as narrow as 54" and as wide as 60", but should be close 56")
The price shown is per linear foot. Enter the number of feet that you wish to purchase in the quantity box then click the "Add to Cart" button. The maximum for 1 piece is 20'. Orders over 20' must be for a 20' piece plus additional to qualify for discounted price."
Ruth