Practical Fishkeeping Diploma - Week 2, Day 1


Welcome to week two of the Practical Fishkeeping Aquarist Diploma. This week is all about filtration, and today we're starting with mechanical filtration.

Week 2, Day 1: Mechanical filtration

Why do we filter? In week one of the Diploma, we looked at water chemistry, and water quality. We looked at the toxic chemicals that fish release into the water around them, like ammonia. A filter is how we, as aquarists, can manage those toxic chemicals.

An aquarium is a confined environment, and any fish inside such a closed system cannot avoid its own waste. In a lake, the waste from fish is diluted down by the vast volumes of water surrounding them. In a river, it is carried away as fast as the fish produces it.

An aquarium doesn’t offer that same luxury — fish in tanks are kept at a density far, far greater than even the most heavily stocked rivers or ponds.

The role of filtration is to keep fish wastes in check by removing, converting or otherwise neutralising them, so that they don’t harm the fish. Understanding how filters function, how to keep them running optimally, and how to avoid accidentally doing something that compromises their function is essential for the aquarist.

Not all filters work in the same way, even if their eventual goal is the same — to remove waste. Getting to grips with these differences will be the difference between a successful tank and a failing one.

Remember: the most relevant parts of this module are highlighted in bold writing, and are extremely likely to come up in the final examination.

Types of filter

While the physical form of filters can vary wildly — there are internal and external canister designs, sump systems that live underneath tanks and are connected by pumps and piping, tubes of moving substrate and even filters that live under aquarium gravel — the way they work can be broken down to one or more of three functions.

These are:

Mechanical filtration

Biological filtration

Chemical filtration

Most commercially available filters will employ at least two of these functions into their designs, while some will have all three. In some cases, a special filter design may only use one filter function, though these are usually aimed at specific duties, such as removing discolouration from the water or for skimming out solid particles of waste.

Mechanical filters

Mechanical filters are filters designed to remove solid, particulate waste. In a strict sense, this is all that a mechanical filter should do.

Mechanical filters usually take the form of foams, sponges, filter wool and mesh screens, though technically any filter that traps out a solid object is a mechanical filter. In some external canister filters, large, non-porous lumps of ceramic media act as mechanical filters for large wastes.

Because mechanical filters physically collect waste, they eventually begin to clog, and this clogging will impact water flows. Left too long between cleans, they may dangerously impact on filter performance.

Tanks with relatively high levels of floating waste (such as those with messy eating fish, or heavily stocked tanks) will need considerably more regular cleans than others.

Some mechanical filters have a finite lifespan until they become clogged to a point where cleaning does nothing. Generally, the finer the filter, and the smaller that particulate it removes, the shorter the lifespan.

Mechanical filters need to be flushed or cleaned regularly. How you clean them will affect how they work. Some mechanical filters need to be cleaned using powerful jets of water, and some sock-type filters for large tanks may even need cleaning in a domestic washing machine.

Other mechanical filters may also function as biological filters, and need careful handling. The foams inside a typical internal canister filter usually require cleaning in old tank water. This involves taking some water from the aquarium in to a bowl and squeezing the media clean in it.

Where mechanical filters are used in a biological role, they must never be cleaned with untreated tapwater.

Click here for next lesson: Biological filtration

How to gain your diploma: Once all the course modules and revision pages have all been posted online, we will open a link to a website that allows you to take your free online exam. If you pass the exam, you will digitally receive your very own Fishkeeping Diploma, to show that you have successfully completed the course, and which is yours to display on the wall near your aquarium, hang in your fish house — or keep somewhere safe where you can take it out and just look at it from time to time.

Note: The Fishkeeping Diploma is not a formal or accredited qualification and should not be confused with the type of diploma presented by colleges, universities and other educational establishments.

Further reading from our sponsors

Filtration for your aquarium

Filtration products for your aquarium

Universal dosing calculator