How to Make a Concrete Block Minnow Tank

Mark the perimeter of your minnow tank onto the ground using landscaping spray paint. The tank can be of any size or shape desired, but for simplicity, keep it to a diameter of 10 feet or smaller.

Dig a hole within the marked location 2 feet deep using a spade. Tamp down the bottom of the hole by dropping a tamp onto the soil to compress the soil. This will create a firm base that won’t shift.

Cut old carpeting to fit the floor and walls of the hole using a carpet knife. Stake the carpeting in place with 8-inch galvanized steel spikes placed every 12 inches through the carpet and into the soil. The liner will create a soft cushion on the base of the tank and prevent rocks or roots from penetrating the bottom of the pond liner.

Line the ground along the side of the hole with a row of concrete blocks.

Cover the carpeting with a layer of pond liner. Press the liner tightly to the carpeting to make sure there’s no voids between the carpet and the liner. Overlap the pond liner over the concrete blocks so that the liner extends about 2 inches past the outer edge of the block row. Fill the liner with water from a garden hose to within an inch of ground level. As you fill the liner, the liner may begin to pull back over the stones slightly as it expands to fill the space. The overlap should ensure that the liner remains over a large portion of the concrete blocks.

Cut off any pond liner still overlapping the outer edge of the stones with a utility knife. Lift the liner slightly from the stones and apply construction cement to the underside of the liner section that will touch the stones with a paintbrush. Press the liner back onto the stones.

Set another row of concrete blocks over the first, staggering the joints of the blocks between layers to prevent them from shifting. Brush the base of the new blocks with the construction cement before placing them over the pond liner sandwiched between the concrete block layers. Add one or two additional block rows to create a higher retaining wall to protect your minnows from being washed out of the tank due to windblown water or flooding.

Set a cinder block onto the center of the tank and place an aerator on top of the block. Run the electrical cord of the aerator to a GFCI plug outlet and then plug the aerator in. Run the aerator for 72 hours to oxygenate the tank water before adding the minnows to the tank.