When shopping for a filter for your new aquarium, or when looking for a replacement filter for the one already on your tank, you are likely to notice nearly every one of the boxes you read will have “recommended for aquariums size XX to XX gallons” in addition to all of the additional helpful point of sale items provided on the packaging by the manufacturer. I liken this recommendation to that of the miles per gallon sticker on the tag of a brand new car, sitting bright and shiny on a showroom floor. Yes, the manufacturer has tested the numbers, measured and metered everything, and has the scientific evidence to prove this is the AVERAGE number for that car’s MPG or in our case filter size for our aquarium. Filters, much like automobiles, are all subject to the whims and desires of their owners. Maybe I want to drive my Honda Civic uphill,  loaded up with five people in it at all times and a trunk full of cinder blocks. I’m going to be on one extreme end of that average miles per gallon, probably quite a bit below what the manufacturer found to be the average. With my new filter purchase, perhaps it is rated for a tank size of 30 to 40 gallons, but I want to keep 200 fish in the aquarium and feed it three times per day. Maybe conversely I only have one small fish in the aquarium which I feed once per day. Maybe I have a normally stocked quantity of fish in the aquarium, but they are all carnivores which are being fed a diet of live fish. The point is, everyone puts different amounts of stress on their filter, so there are things to consider other than recommended aquarium size.

  1. Reef- If using a canister or hang on the back power filter for your reef aquarium, or more than one, the recommended aquarium size on the box is considered way too little by nearly any reef keeper. A filter flow rate which is turning the aquarium over at least four times per hour is generally considered the minimum, and many reef keepers approach the ten times per hour turnover rate. Flow rate, while just one of the many aspects of filtration, is at least a quick check for filter sizing.
  2. Community- The freshwater community aquarium is what most filters have their “recommended tank size” based on. A freshwater community aquarium will have peaceful to semi aggressive fish which are most likely eating flake and pellet fish food with some frozen food supplementation. As long as there isn’t a great deal of overstocking or overfeeding and the aquarium is getting at least one monthly water change, the recommendation on the box will probably be accurate for this type of aquarium.
  3. Carnivore- Carnivores in either freshwater or saltwater are often messy eaters. Fish parts, scales, shrimp or clam parts, all of these things are likely to be only partly consumed by your carnivore. This makes for quite a bit of extra material for a filter to process, on top of the usual biological, chemical, and mechanical activities it already has on the aquarium. If you are keeping a carnivore tank, choosing at least one size larger filter than the manufacturer recommends is the best plan.
  4. Plant-  Live plants can aid in filtering the aquarium quite a bit, so a live planted aquarium can often follow the recommended aquarium size on the box as well. With a live planted tank it is more important to choose a filter that doesn’t too much surface agitation. It is not out of the ordinary for a larger size planted aquarium to have a couple of power heads in it to move water around in addition to a standard size filter.

There are of course other factors to consider, such as filter efficiency, design, what type of filtration a particular filter is best at, but these are topics which are lengthy enough to warrant their own write ups to be addressed at a different time.

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