A bathtub can make an excellent addition to your backyard---as a fish pond. It is large enough to hold a small collection of fish and deep enough so that it will not freeze completely. Above ground or sunk into the earth, a bathtub simply replaces the preformed liner usually used to create a backyard fish pond.
Choose a location for your bathtub fish pond. Avoid placing it in direct sunlight, which will stimulate algae growth in the water.
Clean the tub thoroughly; rinse and dry it out with the towels.
Use a putty knife to seal the overflow drain with silicone. Use a standard rubber stopper to plug the bottom drain so you can easily drain the tub to clean it.
Measure the dimensions of the tub and get digging. Dig a hole big enough to securely hold the tub. You also may choose to leave the tub above ground.
Fill the tub with water. If you are on city water, use chlorine remover to treat the water.
Install a small, submersible pump and filter.
Add your fish. Choose small, hardy, native species such as rosy red minnows, fathead minnows or mosquito fish.
Help keep the water clean by adding water plants such as lilies, floaters and submerged plants.
Top off your fish pond with water daily. Clean it out once or twice a year or when there is abundant algae growth.
Make sure your water is chlorine-free, as any chlorine likely will sicken or kill your fish.
Do not keep koi, as they will outgrow the bathtub pond very quickly.