In a previous article I explained you how to build a mechanical filter type swirl filter. I even offered you a step by step training available here:

As previously explained, the aim of the swirl filter is to separate the solids from the water using gravity and centrifuge forces. I highly recommend you to watch the previous video here:

The mechanical filtration is very interesting especially if you have a high density of fish as it will “clean your water”. You may be wondering “I thought the fish poo was good for aquaponics and was the food for the bacteria and the plants?”. Yes this is correct, in aquaponics we have no waste and recycle everything but we must keep a balance between our different populations. Generally we produce enough nutrients for the plants with a very low quantity of fish. Then if you increase the quantity of fish you will see 2 things:

your nitrate concentration will increase. If the quantity of nitrate released is higher than the consumption from the plants, the nitrate will continually increase. This can easily be managed by using some water for watering your classic garden.

your growbed may clog. As the bacteria population grows on the grow bed media, they form a slimy material called “biofilm”. If a large quantity of organic matters are accumulated in the growbed, they may clog the space between the media. This would lead to serious problems as it would stop the water circulation but also the aeration. As you probably know, the bacteria needed in aquaponics require oxygen to survive (they are called “aerobic” bacteria) and perform their job (called biological filtration). If the grow bed clog, the population of aerobic bacteria will decrease and the fish waste will not be transformed in nitrate. The toxicity of the water will increase and you risk to lose your fish.

Also the plants growing in the grow bed will find their roots in an environment with low oxygen concentration and will suffer and stop growing.

Now you may wonder, is the quantity of particles really significative and is the mechanical filtration a real plus for the setup? The response to this question is dependent on the biomass ( of fish you have in your fish tank. In this video you can see the quantity of “mud” trapped in the filter in 3 to 4 weeks. The system contains a fair bit of fish and a 2 meter square growbed so it gives you an idea of the efficiency of the filtration.

The other positive point of the mechanical filtration is that it allows to trap the excessive fish waste and to use it positively as a natural fertilizer in the classic garden.

An improvement can be added to this swirl filter by simply adding a little tap on the bottom of the swirl filter drum. It will allow you to collect the solids easily instead of having to siphon it.

I hope this video will inspire you to add a mechanical filtration to your setup.

If you are new, you will probably be interested to discover the six steps to build and manage an Aquaponics system. Click here to access for free! Thanks and good reading 🙂