As I set up the new 55g tank, I thought it might be worth mentioning one of the potential hazards of filters - a leak. If you keep fish long enough, you will inevitably have a filter leak of some kind, regardless of the brand and regardless of the filter type. Large leaks are easy to spot and are rather infrequent. Small leaks on HOB filters are often discovered by a drip from the power cord at the base of the loop, if you have a drip loop. And because HOBs aren't very large filters, it usually doesn't take much effort to identify the location of the leak. It's usually occurs in one of two places: the seal where the pump housing connects to the filter body or a crack in the plastic filter body itself.
In canisters, a large leak on the input end will typically allow too much air into the system, slowing or stopping the flow of water. It's the small to really small leaks that typically go unnoticed for a while. However, small leaks in canisters can come from several different connection points. One easy way to quickly spot a small leak, especially one that originates from the hose connections at the canister tap or the pump head seal, is to place a piece of newspaper under the canister. Newspaper will turn dark with just a little moisture, making it a great indicator of water. Newspaper is even better when used in black or really dark wood cabinets where non-pooling water is difficult to see. This works well for sumps also, but sumps can be pretty large and difficult to get newspaper under without some help.
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub