The World's Most Trusted Source of Information About the Fascinating World of Fish keeping

Jump to Site Navigation

Book Excerpt: The Simple Guide to Freshwater Aquariums

by TFH Magazine on December 16, 2011 at 10:00 am

The Simple Guide to® Freshwater Aquariums (Second Edition) is the key to becoming a dedicated aquarium hobbyist is to succeed with your first aquarium. The Simple Guide to® Freshwater Aquariums concentrates on providing you with a complete plan and all the information you need to choose and use the right-for-you aquarium equipment and the right-for-you fish and plants: it wants you to succeed. The information is presented in a completely straightforward text that’s easy to read, easy to understand – and very definitely easy to put to good use.

About the Author:

David E. Boruchowitz is in his sixth decade of fishkeeping. He wrote and edited for T.F.H. Publications for more than a decade and has authored a large number of books on a variety of topics. He also served as Editor-in-Chief of Tropical Fish Hobbyist Magazine.

Excerpt from Chapter 5: What Options Do I Have?

Hang-On Outside Filters

The hang-on outside filter is the most popular and versatile design, and it’s the one I recommend for your first aquarium. This filter has undergone a lot of improvement since the early air-driven models, which were nothing more than a box filter hanging on the back of the tank. They were fed with siphon tubes, and an airlift returned water to the tank through the filter medium. Modern power filters use a water pump to draw water up from the tank and into the filter, where it flows through chambers of filter media and returns by gravity overflow to the tank.

Although there are models available that contain chambers into which you can heap the filter media of your choice, most filters today have modular filter components that you can mix and match and slide into the filter sections. That makes it much easier to service the filter, and it also ensures that water will not find its way around the media instead of going through them, since the medium cartridges fit snugly into the compartments.

Usually a particular filter is available in a series of sizes, each successive one being both larger (and thus having more room for media) and more powerful (in having a stronger pump that delivers more gallons per hour). The idea here is that you can buy a filter sized to your particular aquarium. My suggestion is that you ignore such advice and choose one of the largest models. What?

First of all, you get more filtration for your dollar with the larger ones. Second, if you later upgrade to a larger tank, the larger model may still be adequate. Third, there is basically no such thing as too much filtration. An absolute minimum would be a unit that delivers a flow rate of five or six times the tank volume per hour, but ten times is even better. This is mainly because of biofiltration—more flow means more bacterial contact with more oxygenated water. It also improves the aeration of the water, making sure oxygen levels stay at optimum levels for the fish throughout the tank.

Last but not least, the ratings on most filters are nearly useless. Typically you might see something like “for aquariums of 10 to 60 gallons.” A filter truly adequate for a 60-gallon (230-liter) tank would have a flow rate that would overpower a 10-gallon (40-liter) tank. Although I said that it’s not possible to over-filter a tank, you also do not want the flow rate to be so powerful that it creates a whirlpool effect, with the fish being whipped around the tank all the time. The real problem, however, is that it is unlikely that the filter actually has an effective flow rate of 300 gallons per hour (gph), making it unsuitable for a 60-gallon tank. But even the gph rating can be misleading. The filter’s pump may be rated at, say, 150 gph, but that doesn’t mean that 150 gallons go through the filter every hour. Just pumping the water through the empty system will cut down on the flow; even the introduction of new media will reduce the flow, and as the filter gets dirty the flow decreases even more.

So what do you do? The solution is to buy the biggest and most powerful power filter you can. If you can hang it on the tank, it’s probably not too big. I have very successfully used a spare 400-gph filter on a 20-gallon tank; when I no longer needed it there, the filter went back on a 55-gallon tank. The filter was slightly narrower than the back of the tank on which it hung, but it worked very well. An even better idea is to get two power filters, each big enough to handle the tank alone. Not only does this give you greatly improved filtration and aeration, but it also provides a backup if one filter suddenly breaks down, and it permits you to clean them on an alternating schedule, minimizing the loss of biofiltration capacity. Remember, there’s no such thing as overfiltration, only underfiltration.

Canister Filters

Canister filters have some superior characteristics, but they are the most expensive way to go. One of their preferred characteristics is that they can be placed away from the aquarium (usually under it) and are connected to the tank by hoses. This means that the tank can be placed almost flush against the wall, since there only needs to be enough room for a couple of pieces of tubing behind it.

The major filtration advantage canister filters provide is that the water flows through them under pressure. This is because the filter is a closed system. Water is drawn from the tank and then flows into the filter, through the media, and back to the tank. It is driven by a water pump that, depending on the particular design, is either integral with the filter canister or plumbed into the system. This means that considerable power can be generated, which in turn means that the water is forced through the media under pressure, providing maximum filtration benefits. This also permits in some models the use of diatomaceous earth (a powder made up of diatom skeletons) as a filter medium; water will not really flow through it, but it can be forced through it under pressure. Diatomaceous earth filtration is meant as a temporary filter to “polish” the water—the diatomaceous earth cartridge is replaced by a regular mechanical medium for full-time use.

Canister filters work well and are excellent for large aquariums. They don’t do much that a couple of high-power outside power filters can’t do, but they are very efficient filters, and many aquarists prefer them, despite their complexity.

Most of that complexity is simply plumbing, since you have to get water from the tank to the canister and back again. There are many options in how you set up a canister filter, which is why some of them do not include fittings, which have to be purchased separately. Fortunately, the major brands currently on the market all include fittings and tubing. Many canister filters have several options for the return, from simple tubing outlets to spray bars that diffuse the return flow over the entire surface of the tank.

Whatever filter you choose, if it does not have a true wet-dry option, you should use a sponge filter, add-on rotating contactor, or other biofilter in addition to it.


Recently “wet-dry” filters have enjoyed greater popularity for use with freshwater aquariums, although they have always been used mainly for marine aquariums.

Just what is wet-dry, anyway? Well, obviously, if filters are filtering aquarium water, they cannot be dry, but the name makes sense because these filters make use of a medium that is kept moist but not fully submerged in water. This is the “dry” part of the filtration process.

The purpose of this type of medium is to increase biofiltration, which it does significantly, because air has much more oxygen in it than the most highly oxygenated water does. With the vastly improved oxygen supply, many times the number of bacteria will grow in a given area, and they will process wastes at a much greater rate.

The design of wet-dry filters is quite varied, but they share the feature that somehow water is dripped, splashed, sprinkled, trickled, or sprayed onto a high-surface-area medium, through which it percolates before returning to the tank. Some power filters incorporate a wet-dry section as the final stage, but there are also some that claim to do so and don’t.

Excerpted from The Simple Guide to® Freshwater Aquariums (Second Edition) by David E. Boruchowitz. © T.F.H. Publications. Used by permission.

Posted in Aquatic Books by TFH Magazine on December 16th, 2011 at 10:00 am.


2 Replies

  1. Hi dear,
    I really like this book, its having lots of information and useful tips for the fish and the aquariums.

Leave a Reply

Back to Top

Back to Top

Back to Top

Site 'Breadcrumb' Navigation:

Back to Top