Leeches make fascinating and unusual aquarium inhabitants. Though not as colorful or flashy as many aquarium fish, their eel-like appearance and their reputation for drinking blood put them in a class by themselves. A few leeches in a 10-gallon aquarium are sure to get noticed and to stimulate discussion in a classroom or in your home.
Leeches can tolerate a wide range of temperatures and can live in water that is anywhere from 40 to 80 degrees, though 60 to 70 seems to suit most of them best. If you replace their dirty water or top off the tank with fresh, it's best to use water that's as close as possible to the leeches’ current environment so you don’t shock them too much.
According to the experts at Niagara Leeches, these critters can tolerate a lot of togetherness -- 50 of them can live comfortably for a long time in a gallon of water. Not all leeches can handle that much crowding; some types of leeches, especially those caught in a pond, do best if there are no more than one or two leeches per gallon. If you buy your leeches from a supplier, give them the space the supplier recommends.
Leeches may get sick or even die from chemicals that are routinely found in tap water. Chlorine is the most common problem, but it's one that is easily remedied. Fill a jug or other container with chlorinated water and let it sit out for a day or two, until the smell of chlorine fades away. Filters that screw on the tap and remove chlorine also take care of the problem. Don’t use distilled water, since its complete lack of minerals is also harmful to leeches.
Leeches need to have their water at least partially changed frequently. If you have a lot of them in your aquarium change the water every three days, but if they’re not very crowded then every six days should do. Keep a close eye on their water and change it when it looks dirty no matter how many leeches you have in your aquarium.
Leeches don’t need to eat very often, and most of them can go for months without a meal -- sometimes as long as a year -- but feeding captive leeches once a week is ideal. Meal choice depends on what kind of leeches you have. Most pond leeches will feed on pond snails placed in the aquarium. They’ll also eat frog eggs and earthworms. Leeches purchased from medical supply centers may require a different diet, such as fresh beef liver. Frogs and fish are also important food sources for many types of leeches.