How many times have you heard or read advice something like this, “Make sure your tank has two heaters rather than just one large one in case one fails.” Yes, it’s good to be redundant, but not just when heating your tank(s).
I like to be redundant with filtration and, sometimes, water movement. The argument that you can’t have too much filtration is only partially true. Typically, lots of filtration, especially from impeller-driven filters, creates lots of water movement. This isn’t always a good thing, unless you’re keeping pikes or other fast water cichlids. However, water movement in moderation is a good thing.
Let’s face it, every aquarist will eventually experience an equipment failure. The effects of the failure will depend on many factors, not the least of which is the particular piece of equipment that fails. The ultimate negative effect of failed equipment is dead fish.
Instead of using a single, large filter, consider two smaller filters. If you’re dependent upon powerheads to agitate the water surface, use two small ones instead of a single large one. Redundancy will ensure that a failure won’t doom your livestock. Nothing is worse than going a way for a couple of days only to return home to a tank of dead fish because your single heater or filter bit the dust.