Homemade Tap Water Filters for Koi Ponds

Tap Water and Chlorine

• One of the primary reasons that koi ponds need filters for tap water is that tap water has usually been treated with chlorine. Chlorine is harmful to fish and aquatic plants, and needs to be removed from the tap water before it can safely be used. Activated carbon filters are effective at removing chlorine from water. Activated carbon is made by subjecting a carbon-heavy substance such as coconut shell, wood products or bituminous coal to steam and 2,300-degree temperatures. It is then crushed to produce a granular material.

Activated Charcoal

• There are two types of activated charcoal filter. One of them forces water in a line through the charcoal at pressure. The other simply pours the water through the carbon granules. This second type of filter could be made at home, using a plastic bottle filled with activated carbon. The carbon granules absorb the chlorine by chemical reaction as the water passes over it, so the more charcoal used, the better the filtration.

Alternatives

• This is not the only way to remove chlorine from tap water, however. Chlorine is a very volatile substance. Water circulation and exposure to air will remove it without filtration. Using a garden hose to add the water to the pond should provide enough aeration to reduce chlorine levels. Use 1.5 to 5.3 grams of sodium thiosulfate crystals for every gallon of water to remove chlorine without aeration or filtration.

Biological Filtration

• The other reason that tap water needs to be filtered is biological contamination. Chlorine treatment reduces biological contamination, but does not necessarily completely eliminate it. Additionally, the koi and plants will create their own contaminants in time. You can make a homemade filter for your koi pond by cutting inlet and outlet holes in a heavy-duty plastic container with a lid. Fix layers of aquarium filters and/or fiberglass furnace filters under the inlet. Make sure that you use fish-grade silicon to seal the joints of your filter, to avoid poisoning your fish.