Shop › Bio-Trays Bio-Trays from $6.20 Sold Out Under gravel trays to encourage natural biological filtration in aquariums Pack: Select Pack 5pc 10pc 15pc 20pc 50pc Size: Select Size 6 1/2 x 7 1/4 Small 1 7 1/2 x 7 1/2 Small 2 7 1/2 x 8 3/4 Small 3 9 x 9 1/4 Medium 1 9 x 11 1/2 Medium 2 Open 9 x 11 1/2 Medium 3 11 1/2 x 13 1/2 Large 1 11 1/2 x 14 1/4 Large 2 Open Sold Out Added! Under gravel trays to encourage natural biological filtration in aquariums