Aquarium Filtration 101 by Wolf

Aquarium filtration is one of the most hotly debated subjects in our hobby. Everyone seems to have his or her own favorite brand, type or model that’s worked well for them in the past as well as those they have learned to avoid due to bad experiences. The Internet provides us with a very fast way to share these experiences and hopefully to learn from them. The wide range of equipment available to the average hobbyist is staggering in sheer number and variety. This can be intimidating to beginners and even experienced fish keeper’s alike. The intent of this article is to provide enough information to demystify the process and familiarize them with some of the major players without getting into brand bashing. The main goal of water filtration in an aquarium is to provide a healthy environment for our fish and to extend the time between regular water changes. More on that later… We also filter the water to make the aquarium a lot more pleasant to look at. The lakes and streams most of the fish in our hobby originally come from are rarely ever what any of us would call…sparkling clear.The fish don’t mind this natural situation but not many of us would put up with it. Proper filtration can be the difference between an aquarium that is a stunning showpiece and one that more closely resembles an indoor bog. (Note: this isn’t always a bad thing. We have people in the hobby who strive to attain this look.) OK… now that we know what aquarium filtration IS and what we want it to do for us. We just need to learn how to go about it. Basically all Aquarium filtration falls into three established types.

Mechanical Filtration

This is the simplest form of filtration of all and consists of nothing more than running the water through a porous material in an effort to trap as many of the suspended particles as possible. The smaller the openings are in the chosen material…the smaller the particles that are trapped will be and the cleaner the water. So why don’t we just use a fine sheet with microscopic openings? We do…it’s called Reverse Osmosis or RO and produces amazing clean water but there’s a problem with it. Flow rates (the speed water moves through filter media) decrease a great deal as the size of the openings get smaller or as it clogs. Pressure systems use a powerful pump to force the water through these smaller openings at the expense of a lot higher electrical draw. (RO systems generally use the already existing water main pressure of 40 to 65 PSI.) These filter systems are very efficient but are measured in terms of gallons per day rather than gallons per hour. Not quite the sort of turn over rate we’re looking for. Turn over rate by the way is the number of times the aquarium water is replaced in a given time period. (Usually an hour) A 50 gallon tank with a 500 gallon per hour HOB filter will have an 10x turn over rate. The efficiency of the filter system itself will determine just how large a turn over rate you actually need. Biological filtration is the main limiting factor in this. BB need a certain amount of contact time with the water in order to work it’s magic. We compensate for this by running a higher turn over rate. The type of fish kept, as well as the stocking level in the aquarium, has an impact on the turn over rate equation. Efficiency levels of the different aquarium filters vary so there is no hard and fast rule to turn over rates but you can use the following information as a guide.Wet/dry sump systems…….. 3X to 4XHOB filter systems……………4X to 6XCanister filters…………………6X to 8XAll systems on heavily stocked aquariums ……….10X +

Chemical Filtration

Removing harmful chemicals from the water is a lot more difficult than solid waste because they are liquid and can’t be trapped like suspended particles can. Certain materials however attract these chemicals and contain them. Carbon… Zeolite… ECT. These materials are usually placed in flow-through bags or special baskets and the water is then run through them. Not all of the water comes into contact with the Chemical media on each pass but eventually the levels are lowered to an acceptable amount. Carbon does a great job of removing odor causing chemicals out of the water and has also been suspected of lowering the trace levels of growth inhibiting hormones in the water. (This is one of nature’s ways of controlling population in any given body of water and also has a huge effect on breeding.) There is a great deal of debate in the hobby about the usefulness and even the wisdom of running chemical filtration at all times. Both sides have compelling evidence and no clear cut winner has emerged in the hotly contested debate. Personally I think that a small amount of chemical media is beneficial but that in most cases it’s taken to extremes. Chemical filtration media has a natural saturation point as so needs to be replaced periodically. After this happens the saturated media begins to release the chemicals back into the aquarium Also falling under the heading of Chemical filtration are the modification compounds. These are things that are put in the water to produce a desired effect. An example of this would be crushed coral or peat to raise and lower the PH of the aquarium water respectively.

Biological Filtration

This is the ‘BIG DOG’ of aquarium filtration and is what allows us to keep fish in relatively small amounts of water. (Even the largest of home aquaria are tiny compared to a natural environment.) Unlike the other forms listed here… Biological filtration is a natural process that we help along but don’t actually create. The bacteria that do the actual work exist everywhere much like yeast spores. What we do is cultivate them and use them to our own advantage. You can look up this process on line in a lot more detail than I have room to into here but it basically involves little more than providing a home for Nitrosomonas…Nitrobacter… and other beneficial bacteria you probably don’t care to learn the names of… These little guys are the workhorses of the aquarium world. Some of them feed directly on ammonia (this is a good thing) but excrete Nitrites (this is a bad thing) in return. Fortunately their neighbors like to feed on Nitrites (a good thing) and excrete Nitrates. This is far less toxic to fish and can be controlled by periodic water changes although certain types of algae are known to eliminate it and filtration systems exist that take advantage of this to almost eliminate the need for water changes. The process is called the nitrogen cycle or “cycling” for short. All aquariums have to go through this process (From 6 weeks to 3 full months in some cases…) before it’s completely stable. Fish can generally be kept in the tank MUCH sooner than this as long as stocking levels are kept low…water changes are performed regularly and the water is tested frequently to prevent damage to the fish. This would be a good time for a brief note on water testing. Don’t ever let anyone tell you that it’s useless or unneeded. Even though a large number of people keep fish without ever testing either the tank water or the source water that they use for the water changes it’s NOT a good idea. Fish can become sick or even be killed in some cases by moderately high levels of ammonia or nitrites. Some species handle it better than others. Waiting until you see the fish in distress to check out a problem is many times far too late. That’s a short explanation of the types of filtration. What follows is a list of some of the different kinds of filtration systems available along with a short description of how they work. I don’t have the time or space to go into them all of course but I will do my best to cover the most common.

Continuous flush system

This is basically useless to the average home hobbyist and amounts to nothing more than a constant water change. Many public marine aquariums situated along the shoreline use this method on their giant display tanks. This is very little help to a reef tank situated in a living room in the Mid-west. It could however be useful to someone building a large pond on a piece of property with a spring or year round stream. All that's required is an inlet and outlet to the pond and a screen barrier to allow the water to pass while keeping the fish in place. Another way of doing this is to allow the water to sit on its own for a period of time and then to periodically flush the pool with fresh water in a massive water change. A lot of commercial fish breeders use this method on large outdoor breeding ponds. One of the dangers in this kind of breeding is that any sort of natural flooding is likely to allow captive bred species to escape into the local environment. The state of Florida is overrun with introduced species of fish for this very reason.

Sponge Filters

Often called ‘Breeder’ filters, these simple units are unquestionably the most cost effective systems in the world. Consisting of little more than a tubular plastic chamber inside a piece of shaped foam, they can be driven either by a small power head or by an air stone and lift tube. This allows them to be used with portable battery powered air pump and this gives the filters a great deal of flexibility. They can be used in fish transportation boxes, boat live wells, fry tanks and breeding tanks. The low current/ large surface area design make them ideal for tiny delicate fish. Although they are only a marginally effective mechanical filter they can and do keep tanks as large as 100 gallons clean on their own.

Corner Filter

This was one of the first types of aquarium filters in existence. Most of the tanks were small ones at the time…a 30 gallon metal framed tank was considered HUGE. The filter itself is a small plastic box that sits inside the aquarium and is filled with a variety of media and powered with an air stone. Although it’s far superior to the sponge filters in both mechanical as well as chemical filtration it has very poor biological filtration compared to the massive capacity of the sponge filters. Although they are much less common than in years past you can still find them for sale in most aquarium stores.

Under gravel Filter System

It wasn’t very many years ago that this form of filtration was the backbone of our hobby. It’s mostly discounted now as obsolete but it has a lot of advantages. It worked by placing a plastic plate with slots on the bottom of the aquarium and covering it with a layer of gravel. Pieces of clear tubing attached to the plate created water flow either by air stone or later on by power head. The available BB (Beneficial Bacteria.) surface was large and able to handle moderately stocked tanks with ease for many years with little or no service at all. From a biological filtration standpoint it worked well. All of the fish waste and uneaten food were pulled by the water current down into the gravel and held to either decompose or be removed by vacuuming the gravel. The main downfall of this type of system was two fold. As fish loads increased the level of BB increased along with them. This tended to clog the filter plates, necessitating breaking down the aquarium. (No big thing if you’re a retail outlet with a line of 45 tanks but defiantly a problem if you only have one or two tanks and they are both full of fish.) The other problem was Oxygen. All true fish extract oxygen from the water to breath. So do the BB… Water is only capable of holding a small fraction of oxygen compared to air. The more of this available oxygen that is used up by the BB: the less of it that is left over for the fish.

Wet Dry (sump) System

This is really a lot simpler than it looks and works amazingly well within certain limitations. Water is skimmed off of the surface of the aquarium and then siphoned out of the tank and down to a water reservoir (sump). A return pump keeps the water level in the sump below a set level and the incoming water from the tank is filtered by a set of washable filter pads (Mechanical) and then trickles over bio-media. (Material designed with a huge surface area for its size as a home for BB.) This constitutes the bio-filtration portion of the filter. You might assume that because the sump is a lot smaller than the original tank that there wouldn’t be enough BB to properly filter the water. The truth is that the sump has a FAR greater biological capacity than the aquarium gravel bed. The huge surface area of the bio media combined with the massive amount of oxygen available in the air makes the wet/dry system the best biological filtration available. They have two deficiencies however. Because the system is gravity fed there is a limit on how fine you can go on mechanical media. This is a personal choice however because while a wet/dry may not polish the water the way a DE or pressure filter would it still does a good job of cleaning the water because of the volume of water moved. The other problem with them is that it’s difficult to create flow patterns in the tank and most of the accumulation of debris on the bottom of the tank is untouched. The first problem is addressed with the addition of power heads (small submerged pumps that move a lot of water around.) Gravel vacuuming takes care of mulm build up.

Hang On Back Filter Systems

HOB units are designed mostly for convenience but have evolved over the years into some very useful tools. They are generally a good low cost alternative for smaller tanks. They work by pumping water out of the tank by way of a pick up tube and then through a pad or series of pads and then back into the tank by way of a ‘waterfall’ type outlet. These kinds of filters do a very good job on small to medium sized tanks and are even a welcome addition to larger ones but they have a few drawbacks. The water returns on most HOB units are noisy and they tend to vibrate. Additionally the replaceable pads that make servicing the units so convenient and fast are an on-going expense. A lot of hobbyists either make their own clean-able pads or modify the filters to use cheaper substitutes.

Canister Filters

A canister filter is a self contained remote unit that connects to the aquarium by hoses. The water is moved through the filter media in the body of the sealed unit and then returned to the tank. One of the advantages of this design is that they can be used in installations with very limited space. They have a much larger capacity for filter media than the HOB units but the media is never directly exposed to the air, thus limiting the efficiency of the bio media inside them. They have a lot higher flow rate than the HOB units and can go for much longer periods of time between servicing. Canisters are a sealed system and this allows them to provide a greater mechanical filtration than other common types of filters although this is limited by their lack of a true pressure rated pump. They are unfortunately much harder to clean when the time comes for a service. The units have to be turned off…disconnected from the hoses…and moved to another area to be cleaned. The difficulty of this process varies from brand to brand but in general they are all fairly close to the same. After servicing is complete the canisters must be purged of air to operate properly and with some units this can be a problem.

Sealed Pressure system

These are generally a professional grade filtration instillation and not frequently seen in home aquariums. They use hoses and sealed canisters much like a self powered canister system but they are much better built and are driven by far more powerful pumps. Because of this extra pressure they are most effective mechanical filters you can use on an aquarium. Cleaning is made simple by the fact that they can be back flushed of debris without ever opening the canister. (I personally know of several of these systems that have been operating continuously for over 20 years.) Chemical and Biological filtration are handled by separate chambers all connected to the same pump. Many of these sealed pressure systems have provisions for built in Ultra Violet sterilizers and remote tank heaters. The plumbing of these systems allows for the simple automation of routine service tasks like water changes and back flushing. In large planted systems remote co2 injection and even trace element addition and water quality monitoring can be incorporated. Very expensive, you can be sure, but defiantly state of the art filtration with unmatched performance.

Organic Systems

These systems fall into three main types so I’ll cover them separately. They all share one thing in common. All of them are based on living organisms. (BB falls into this category as well.) These are not very common so I won’t go into a great deal of detail on these.

- Algae Based Systems

These systems use very long runs of clear vinyl tubing and specific frequency light to grow and maintain beneficial Algae that can even convert and eliminate Nitrates and other trace elements from the water. Manufacturers claim that these systems are so efficient that a single 25% water change is all that’s required per YEAR…Mechanical filtration is handled by a simple pre-filter and the whole thing runs on a very low draw pump.

- Hydroponics’ based systems

These are relatively new and quite specialized central systems (multiple tanks on a single filter.) based on the concept of the plant filter. Tank water is pumped to a remote location…pre-filtered and then circulated through long hydroponics trays. The plants extract nutrients from the water and in the process remove all of the harmful elements. Because of the large amount of water loss from evaporation in these systems water changes are unnecessary because of the constant addition of fresh water.

- Live rock based systems

This is no doubt the most natural system available and uses live coral to filter the aquarium water. It requires a delicate balance to maintain but once established can be run for years with little or no major service. Initial water quality is critical and most hobbyists run RO/DI systems Many different combinations of the above systems have been used over the years along with a lot of trends and fads. Water filtration for the home aquarium is as much of an art as it is a science. New equipment is introduced each year promising a revolution in water quality. Once in a while one of the new systems catches on and replaces one of the old standards. This is rare however. No mater what system you chose or what brand you like. All of them are only as good as the person maintaining them. The aquarium filtration equipment we all use in our hobby is constantly being improved and redesigned with an eye towards greater efficiency and convenience.

This Article is contributed by Dane (wolf) and originally posted in MosterFishkeeprs.com.