well, if you gonna use a 15H tank, you can go to HD and by small acrylic sheet, 12"x24", 24"x24" or 24"x36"....etc.
Or call Jfreeman or any other acrylic place and ask them to cut the acrylic on the size that you need.
you dont need the 0.25 acrylic, you can use 0.22 acrylic.
J. Freeman, Inc.
65 Tenean Street Dorchester, MA 02122
(617) 282-1150 or (800) 841-9442
Gustavo