Filter me this, Filter me that...
Ok, we think we have selected a tank and a stand. Now what? Well, it is time to decide on a filtration unit. First of all, there are many to choose and confuse the new aquarist. So, let's try to simplify things. There are basically three types of filtration. These are mechanical, chemical and biological. A healthy aquarium typically will employ all of these methods to some degree.
Mechanical filtration is simply a method, which mechanically filters waste out of an aquarium by drawing waste in via a pump and trapping it for your removal. It does not aid in removal or conversion of ammonia, nitrites and nitrates. They also must be cleaned frequently to ensure that there is no decay of waste within the filter or they will not be serving their purpose.
Chemical filtration is when water is run through a chamber via gravity or a pump. Within this chamber is a chemical filter media such as carbon. Carbon remains to be the most popular method of chemical filtration. It will remove and dissolve waste, as well as keeping the water very clear and clean looking. The one drawback is it will leak phosphates into your system, which can cause unwanted algae growth. Aside from carbon, there are other chemical media, which can be used to absorb nitrates, ammonia, phosphates and more.
Biological filtration is the method in which oxygen rich water is passed over a surface in which "beneficial" bacteria is grown. This bacterial will break down ammonia and nitrites converting them into nitrates. The nitrates are then kept in check during your routine water changes. This is by far becoming the most popular method in filtration. After all, nature taking care of nature is more logical than employing chemicals all the time.
Inexpensive methods of filtration, which may come with some smaller aquariums, are under-gravel, internal power and external power filters. While these methods may be sufficient for smaller tanks with very light loads, they do not offer the type of filtration desired for a large (over 50-gallon) aquarium. First of all, internal power filters are not intended for the main filtration duties. They are still used, but more for the purpose of creating water current through out the tank.
Under-gravel filters, UGFs, are a method of drawing water through the base media or substrate trapping waste within the media as it passes. This can create an effective biological filtration environment as long as the substrate is maintained to prevent clogging in spots. UGFs are popular within the freshwater realm since typically in freshwater, the substrate or gravel is large enough not to fall into the space between the tank bottom and filter panel. However, in saltwater tanks, most people who use substrate enjoy using sand and crushed coral making the ability to use an under-gravel filter difficult. I'm sure some UGF enthusiasts are shaking there heads right now. I will continue to say yes, under-gravel filtration can be a very effective method and can be implemented into saltwater even when using sand. The drawback, however, to any UGF setup, is the possibility of creating "dead spots" below the substrate, where the water flow is too weak. This can lead to unwanted bacteria growth that can harm the water quality and your tank mates. If used in conjunction with a sump or canister filter, it can raise the effectiveness of the overall system, but it must be maintained as with everything else. This can cause some serious headaches if something were to go wrong below the surface. The only way to get below is the removal of your substrate and disruption of your system.
Now the external power filters that hang on the back of your tank, or built into the hood as with the Eclipse systems, can provide sufficient filtration for small systems, and the Bio-wheel filters are actually very decent for very light load set-ups. However, all in all they are not going to be able to handle the load that most Saltwater life demands. If the tank has one there is no reason why you can't continue to use it in conjunction with another, more powerful filter. Remember, if you have basic plumbing skills most of these things can be modified to be incorporated into you system in some way or another. Creativity and problem solving skills are a must in this hobby.
So, with those for the most part being inefficient for most applications by them selves, where does that leave you? Your choices are now Canister Filters or a Wet/Dry Sump, also known as a Trickle Filter.
Canister Filters are external chambers with different levels of filtration methods combined. Water is pulled from the tank via a pump and pushed through the different stages of the canister. The first stage is typically mechanical in nature where a pre-filter pad is used to capture large pieces of waste. Next can be either biological or chemical media to further the process of waste breakdown and removal. Canisters are very effective and if large enough ones are employed they can do a great job in keeping even messy eaters in check. The drawback is they must be cleaned frequently and this is no easy task. Although they have gotten better recently, Canister filter maintenance consists of shutting down the system, removing the canisters and taking apart the filter to clean and replace the different stages. For some, this becomes too cumbersome and time consuming, and it if the filters are neglected, then it is likely that your tank will have major health problems.
So, that leaves us with the Wet/Dry Filter. Not only does this add a little more volume to your system, which is great; I feel is the most efficient and expandable option. This system uses gravity to bring water from the main tank via the overflow boxes. If your tank does not have overflows built in, the Wet/Dry filters usually come with a hang-on one these days. Even so, I would recommend buying an additional one to maximize the area of surface water that meets the overflow boxes. This aids in both filtration and water movement. Once the water enters the overflow from the tank, it then falls through hoses into the top of the Wet/Dry filter where it first meets a pre-filter. This can be simply a filter pad or a carbon, phosphate or ammonia pad. Here large particles of waste are trapped and the rest of the water continues through the pad and trickles down over a section of "bio-balls" or other such biological media. This media is designed to harbor the "beneficial" bacterial essential for the functionality of this system. Here ammonias and nitrites are broken down and converted into nitrate. The water then flows through the section of bio-balls and into the bottom of the sump. Here there is space for more filter media bags or area to introduce heaters, Protein Skimmers, UV Sterilizers or extra chemical power filters. Once the water passes through this area, it is then pulled back up into the main system via a pump. Some sumps are now available with Protein Skimmers built in. Some of these are quite efficient and should be looked into as a possibility from the beginning. Not sure what a Protein Skimmer or UV Sterilizer is? Not to worry, these will be discussed more later on.
Keep in mind, if you do choose a sump, it may or may not come with a return pump. Typically they do not. So, you'll need to purchase one that is rated for your tank size. The general rule of thumb is you want your tank to cycle all the water through the system at least 7 - 9 times an hour. So, simple math would tell you, if you have a 100-gallon aquarium, then you would need a return pump rated at 700 - 900 gallons per hour. In a reef tank, where you have many delicate, "current dependant" animals, such as corals and clams, then it would be wise to move those numbers up to 10 - 20 times an hour. So, your pump for a 100-gallon tank would obviously need to be rated at 1000- 2000 gph. In a perfect world that is simple to accomplish, but there is one factor that must be considered. The distance the return pump has to push the water before it reaches the tank can considerably degrade the flow rate of the pump causing a decrease in the overall performance. If a pump says that it is rated at 500 gph, what that means is, with no resistance and no distance to travel the pump will perform at the optimal rating of 500 gph, however that is not going to be the case for a pump below an aquarium trying to push water vertically. This is not that drastic an issue really, considering most returns are only traveling a few feet. It defiantly is a concern for aquarists who place their filtration in basements or other rooms. These days a lot of manufacturers are placing ratings on the box illustrating the flow rate at 0 feet, 3 feet, 10 feet etc. Everyone will have differing scenarios. So, just do a little investigating and it should be easy to determine the pump right for you. Without doing a bunch of math, a logical thought process would be to get a pump rated for a bit higher than your "target" gallons per hour to compensate for the extra resistance. Keep in mind that this will also apply to other units, such as canister filters. They too need to be rated for your "target" flow rate. So, factor in the distance the canister's pump has to push and it will not hurt to purchase one rated for a slightly larger tank.
For now, just concentrate on picking the right filtration methods for you. Remember, you do not have to pick just one. As it was addressed earlier, you probably will be incorporating a bit of everything at some point or the other. I believe in the concept that you can't really over filter. Could your swimming pool be TOO clean? Meaning, if you had a 125-gallon aquarium and you were looking to buy a sump. You could pick from ones rated for tanks up to75-gallons, 100-gallons, 125-gallons and so on. Obviously you never want to go lower than your tanks specifications, but there is no reason you cannot go above. If you have the room and the extra money, purchase one suited for the next larger tank. All you would be doing is adding even more volume and room to expand your filtration system within the sump.