My cichlid tanks are heavily stocked and therefore require heavy duty filtering to ensure that the aquariums' inhabitants stay healthy and are not subjected to polluted water. From day one, I decided that I wanted large, efficient, reliable filters for my aquaria. This, to me, meant buying Eheim external filters.
Aquarium filters have three possible functions: chemical filtration, mechanical filtration, and biological filtration.
Chemical filtration is not often used, but can be utilised to adjust water conditions (adding peat to soften water, for example).
Mechanical filtration is removal of solid particles from the water. This is the function that many beginners think is the most important, but it's not.
Biological filtration is critical to ensure that the fish can survive. Fishes produce waste which breaks down in the water to deadly ammonia. Biological filtration converts this firstly to less toxic nitrite, then to the much less toxic nitrate. The nitrate is removed during water changes ensuring that there's no build up of pollutants in the water.
Without efficient biological filtration, most fish will not last a week in an aquarium and 'nitrogen cycle mismanagement' is the most common cause of fish deaths in new tanks.
There are two main factors that govern how efficient a filter will be; water throughput and filter media capacity. The water throughput determines how much food and oxygen can be delivered to the filter. The amount of media packed into the filter determines the amount of beneficial bacteria that can colonise the filter and thus how much waste can be processed.
The Eheim 2217 is supplied with all the required hoses, clips and taps. It has a capacity of six litres, and was supplied with seven sponges. These provide excellent mechanical filtration and a massive surface area for the beneficial bacteria to colonise. With the sponges in place, there is still around 40% capacity remaining in the filter which means that extra filtration packages can be installed if required.
Bags of nitrate remover, polishing agents, water softeners or hardeners are simple to add to the filter as and when required making this unit extremely flexible as well as efficient.
The filter's throughput of 264 gallons per hour (when free of media) means that the water in my tank is 'turned over' at least three times per hour. This means that any waste is quickly delivered to the hungry filter bacteria, giving a very short residence time for ammonia/nitrate in the aquarium. Since setting up the aquarium, I've never detected any trace of ammonia or nitrate.
Maintenance is straightforward, simply turn the filter off, close the isolation taps, and remove the filter top to get at the media inside. This does reveal one of the filter's two weaknesses. The head is held in place with six small metal clips. These are fiddly to remove and always seem on the verge of snapping (they haven't yet, however). More modern filters from Eheim have a better arrangement here.
My routine for cleaning involves filling a bucket with tank water (don't use tap water, the cold water can shock the bacteria and the chlorine can kill it) and rinsing the sponges out into the water. This water is then discarded and the process repeated. In this way, the waste is removed and the bacteria not harmed. The sponges are then returned to the filter.
Restarting the filter reveals its other weakness. The 2217 requires manual priming which can be a soggy, frustrating job. The newer models have a much better system for this.
I chose Eheim for their legendary German build quality and reliability. This filter has been in continuous operation for six years and the only maintenance required has been regular cleaning (around every three months in my tank).
A slight noise has developed which appears after cleaning. I think this is due to wear on the impeller. The cleaning removes a layer of muck which allows the impeller to move slightly. This disappears again after a week or so and could be cured with a new impeller.
The 2217 cost me £120. This filter has been excellent value for money over the last six years. It can now be bought from www.zooplus.co.uk for only £76. There are newer Eheim models, but whilst they're easier to clean, are more expensive. It is, therefore, up to the purchaser to decide whether the newer models are better. For a no nonsense, high quality filter, the 2217 is hard to beat.
Finally, a tip: don't throw your waste tank water down the drain. This water, loaded with nitrates and phosphates makes excellent fertiliser (especially the water from filter cleaning). Throw the waste water onto your garden, it's a form of recycling and your plants will thank you for it!