Why You Should Keep Your Existing Aquaponics Aquarium Filter


In a normal aquarium, a water filter is a must so that the fish are protected from the very waste they produce. However, you are usually led to believe that in an aquaponics system, the plants act as the filter, making a regular filter redundant. However, the fact is that when you are converting your regular aquarium to an aquaponics set up, it may not be such a bad idea to leave the aquaponics aquarium filter in place. Now you must be asking why that is… and we’ll look at a few facts now…

Photo Credit: Geek2Nurse via Compfightcc

Photo Credit: Geek2Nurse via Compfightcc


Why keep this filter?

There are a number of reasons for this. Firstly, initially the plants will take some time to take root. In this period, you will still have the required number of fish in your tank. But the plants still being very small, they will not have need for quite as much nutrition.

Naturally, at these stages, some of the fish waste tends to build up and makes the water look murky. In fact, if you were to check out aquaponics beginner’s forums, you will find many people list this as a concern because they think the system is not working. While the system will eventually pick up its pace, why harm your fish in those first few days by letting the harmful waste build up in the water. As a result, in those first days your aquaponics filter is a good thing to have.

On the other hand, not all aquaponics systems will follow the same uniform pace of growth – or will even be successful. If you think that it will work out on the very first go, you’re probably setting yourself up for big disappointment. Instead, know that the plants could fail for a variety of reasons – and the fish may also not take to the system quite as easily. In either case, an aquarium filter can save you the trouble of ending up with a handful of dead fish. It will ensure that the water stays clean so the fish thrive – even as you continue to try with new saplings.

Photo Credit: Mananasoko via Compfightcc

Photo Credit: Mananasoko via Compfightcc


Now, besides these needs, there is some amount of filtering that even an aquaponics system needs…

What sort of filtration will your system continue to need?

In any aquaponics system, it is said that the plants are good for picking up the fish waste. But this is actually wrong. Fish waste is actually ammonia, and plants don’t actually absorb any ammonia. Also, plants just pick up the minerals and a form of the ammonia, but that’s not the only waste you’ll have in a system. Here are three kinds of filtering that are essential:

  • Mechanical filtering – mechanical waste refers to any solid waste in the tank – dead fish, food that is not eaten by the fish, dead fish, pieces broken off from the aquarium decoration, and even small bits of the grow media if they’ve found their way into the tank. None of these will be automatically filtered out in an aquaponics system, and as such need to be dealt with.

  • Chemical filtering – the minerals are good for the plants. But then there are other chemicals like lead and heavy metals which are neither good for the plants nor for the fish. These will affect the quality of your yield from the system – provided you are raising the fish and growing the plants for consumption. And as such they need to be filtered out using activated charcoal. However, keep in mind that activated charcoal cannot distinguish between bad minerals and good minerals, and should only be used sparingly and periodically – to cull the tank. Thereafter you need to again let the waste build up for the sake of your plants.

Photo Credit: Waleed Alzuhair via Compfightcc

Photo Credit: Waleed Alzuhair via Compfightcc


  • Biological filtering – The fish release ammonia, as we mentioned earlier. But this ammonia needs to be broken up into first nitrites and then nitrates so that the plants can then absorb it. To do this, you need a colony of good bacteria living in the system – usually based on porous material like sintered glass or coarse sponge. This is also a filtering of sorts – and one that is essential in an aquaponics system. However, in many cases porous grow media used can also serve to house this bacteria and serve both purposes at once.

And finally, let’s take a quick look at…

How to incorporate basic filtration into your system?

The best bets in an aquaponics system are sump filters and external canister filters. What you want from them is:

  1. It siphons the water out of the tank and removes all solid sediments from it.
  2. It then passes it through your biological filter.
  3. The water is then delivered into your grow bed.
  4. Once circulated, a bell siphons takes the cleaned water back into your fish tank.

Many people also include a separate tank with duckweed in it – and they circulate the water through that immediately before transferring to the tank. In this way, any trace minerals and nitrates are picked up by the weed. And in addition to having an extra bio filter, you also have a cheap source of good food for your fish.

No, an aquaponics aquarium filter isn’t really a must – because the chemical and mechanical waste can be removed periodically – and the bacteria usually will take up residence in most porous grow media. But if you do have a filter at your disposal – do not waste that. Use it for the best results!

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