Philosophy of Aquarium Filtration
These are some of my thoughts on filtering aquariums. I don't claim to be an expert, but this system has worked well for me in raising a variety of African cichlids.
One of the main problems in the aquarium hobby is that all of the recommendations, from tank size to filtration, are focused on the very bare minimums. This leaves no margin for error and leaves a lot of disappointed budding aquarists when things go wrong... which they inevitably do. In addition, most new hobbyists treat these recommendations as an "ideal" setup, and try to push the limits one way or another. This process is further compounded by many pet shops listing the requirements for fish at the size they are selling instead of the adult size. This leads to recommending 30 gallon aquariums for Oscars (should be 75), or 20 gallon aquariums for "mixed" African Cichlids (depending on species should be anywhere from 55 to 125). The aquarium shops don't mind, as people get used to fish having a life-span of 6-9 months and just buying new fish when they all die. If this were any other pet, there would be mass outrage. Imagine if someone were discovered raising 2 rotweilers, a pit bull, and a German Shephard in a walk-in closet. It would be in the national news as severe animal cruelty... however, this is roughly equivalent to many aquarium setups sold every day by pet shops. But I digress.... this article is about filtration not tank size. Needless to say, I believe that the recommended tank sizes on filtration packaging are insufficient.
There are three types of filtration that are generally desirable in an aquarium - mechanical, biological, and chemical. Mechanical filtration is about removing particles from the water to keep it clear and keep decaying matter from fouling the water. Biological filtration involves maintaining bacteria colonies to convert ammonia to nitrites and then to nitrates. This is what is developed in the process of "cycling" a tank. Chemical filtration can remove harmful chemicals from the water. Chemical filtration is often misunderstood, as most filters come with a packet of activated carbon. What they don't tell you is that after a few days that activated carbon is "used up" and provides no additional chemical filtration. Fortunately, most aquariums don't require chemical filtration and the carbon can remain in the filter to act as additional surface area for biological filtration, albeit not as efficient as material optimized for that purpose. The main use of chemical filtration is removing medications after they have run their course. I generally do not use the activated carbon that comes with my filters, substituting either a sponge or ceramic material for bio-filtration.
There are two main types of filter that I will discuss here, hang-on-back (HOB) filters, also known as power filters, and canister filters. I do not recommend undergravel filters as they are almost never maintained properly and when improperly maintained can lead to toxic buildup in the tank. They are also not generally sufficient for African cichlids. Another type of filter that I will not discuss are sumps. I think sumps are great for large tanks, but by the time people are ready to set them up they have usually done enough research that they don't need an article like this.
HOB and canister filters have different tradeoffs. HOB filters generally offer much better mechanical filtration, whereas canisters offer a larger volume of material for biological filtration. HOB filters are often easier to clean and maintain. Canister filters are generally quieter and less visible in the tank. HOB filters provide more aeration. I think there is a place for both in the modern aquarium. For brands, I like Aquaclear HOB filters. I've tried several varieties of "bio-wheel" filters and never had much luck with them. The wheel always seems to clog up. If you are overfiltering as I recommend, you don't need the wheel. I'd recommend two different canister filters depending on your budget. If you don't mind the cost, Eheim makes the best canister filters. I generally use Rena Filstar filters, however, as they are almost as good and much cheaper. Again, going for quantity over quality. I've also heard a lot of good things about Fluval, but haven't used their canisters. I wouldn't worry too much about brands for canisters as the mechanism is fairly simple and I think all the main brands are decent.
The next question that arises is, how much filtration do you need? Keep in mind that I keep African cichlids which are messy and generally heavily stocked. These recommendations may be inappropriate for delicate, lightly stocked fish that are sensitive to water movement. With that in mind, my recommendation is to try and turn over the volume of water in the tank 10 times every hour. The recommended sizes on most filters work out to about 5 time per hour... but there is a catch. Those ratings are based on running the filter with no media. By the time you load it up with appropriate media the flow rate is greatly reduced. I usually figure a fully loaded filter runs about half its rated flow. This leads to aiming for about 4 times the recommended filtration on an aquarium. For example, an Aquaclear 110 HOB filter is rated for a 110 gallon tank. It is supposed to turn over about 550 gallons per hour. I use 2 of these on my 55 gallon mbuna tank. I always recommend using 2 or more filters on a tank rather than one that is rated twice as high for reasons that will become clear.
This is definitely over filtered. However, as I hinted in my introduction, it provides a number of benefits. Firstly, you don't have to worry about how much biological capacity your filters have. If you follow my recommendation, you'll have more than enough with some to spare. Similarly, the high level of mechanical filtration will keep your water crystal clear.
Think about the failure modes for this system. Filters inevitable fail at some point. In my system, you can have a failure and still be well over the recommended level. This also allows you to alternate cleaning the filters without worrying about accidentally cycling the tank (although you should still follow good practices and clean the media in aquarium water instead of tap).
Another huge advantage of this system is that you never have to cycle another aquarium. Once you have at least one aquarium up and running, you are set.
Here are two new-aquarium scenarios. In the first, we are adding a new aquarium with new fish. The process is to buy appropriate new filtration for the new aquarium, but instead to place one of the new filters on the new aquarium and one on the old. When the fish arrive, take one of the old filters off the old aquarium and install it on the new aquarium as the fish are added. Bingo, no cycle and everything runs smoothly. This assumes of course that the aquariums are of similar size and stocking level.
In the second, we are upgrading our main tank to a larger tank and adding stock. Just install the larger tank and move over the existing fish and filters. Buy new filters and fish as appropriate. The extra capacity of the older filters will easily handle the new load with no cycle.
The reason this works is that bacteria reproduces by roughly doubling. Here is an extremely simplified example. Lets assume that your fish load requires 32,000 bacteria (not a realistic number, just used to illustrate) to process the ammonia. When you cycle the tank, lets say you start with 1 bacteria. The next day you have 2, and so on.
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13 - 14 - 15
1 - 2 - 4 - 8 - 16 - 32 - 64 - 128 - 512 - 1k - 2k - 4k - 8k - 16k - 32k
It took 15 days to build up enough bacteria to process the ammonia to nitrite. We then have a similar wait to build up the bacteria colony to process the nitrites to nitrates... this is the month long cycling process that most of us are familiar with.
Now, lets assume that we've cycled the tank and the bacteria is evenly distributed between our two filters. Now, we buy a new tank and add a similar number of fish to it. We move one old filter to the new tank and add new filters to both tanks. Now, both tanks require 32,000 bacteria, but only have 16,000 bacteria. No big deal, that population will double in a day and neither tank will go through a cycle.
Obviously those numbers are silly, but the principle holds. This is one of the main advantages of splitting the filtration in your tank across multiple filters. It definitely beats waiting a month to bring each new tank online.
I'm not saying that this system is for everyone, but it has worked well for me. I maintain tons of filtration on my tanks and new tanks are brought online quickly without any fuss. When I've had the occasional equipment failure, it has been no big deal, and my fish are fine until I get things back in order (filters anyway, heaters are another issue for another article). I also have enough margin that if I am slow getting to my water changes everything works out ok.
I hope this article helps people who are trying to understand filtration and setting up new tanks. I appreciate any feedback and will work on refining this and adding it to an "articles" section of the site along with future articles I have planned.