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Biological filters are the means by which people like you and I are able to grow our own fish.  In short……no bio-filters; no aquaponics!

Bio-filters are simply good places for nitrifying bacteria to live and play.  They provide the optimum environment for the bacteria that convert the potentially toxic wastes produced by the fish into organic plant food.

Bio-filters take many forms.  In a media-based recirculating aquaponcis system, the grow beds serve as bio-filters.  In a raft system, the grow tanks usually foster much of the nitrifying activity. 

The understated hero of backyard aquaculture (and aquaponics), however, is the humble trickling bio-filter.

Now, let me be clear right from the outset, I’m not suggesting that we all dispense with our media-based or raft growing systems. 

What I am saying is that trickling bio-filters will make any aquaponics system more resilient and more productive and that there are good sound reasons for having them…..including:

1.   They provide for much more nitrification than a grow bed of a similar size – simply because they have a continuous flow of water through them as distinct from the intermittent flow of a flood and drain grow bed.

2.  They weigh much less than a grow bed or grow tank.

3.  They enable the staged development of an aquaponics system.  The fish tank can be set up, cycled and the fish added……and then the growing systems can be added as time and resources permit.

4.  They are much cheaper to build than another  grow bed – good for those with a limited budget.

5.  They have a much smaller footprint than a grow bed – good for those with limited space.

Trickling bio-filters come all shapes and sizes

Trickling bio-filters come all shapes and sizes

6.  They will accommodate a wider choice of media.

7.  They offer greater portability – good for people who rent their homes or who are anticipating a move.

8.  They permit greater control over overnight temperature variations in an aquaponics system.  Some people shut their pumps down overnight to limit heat loss out of their system.  While I understand why they do this, it’s a risky practice. The inclusion of a trickling bio-filter into their water column will allow these people to disconnect their growing systems without prejudicing nitrification and oxygenation during the period of the day that it’s most needed.

A wide variety of media can be used.

A wide variety of media can be used.

 9.  They facilitate over-wintering more readily.  Fish can be moved indoors to avoid extreme weather….cold or hot.

10.  They are much easier to maintain than grow beds.

11.  They enable the separation of the fish tank from the growing systems in the event of disease or infestation in either fish or plants – which means that one can be treated without doing harm to the other.  

12.  They provide for more effective aeration – largely due to the continuous water flow.

13.  They are more convenient for ancillary small systems like fingerling system purge tanks or quarantine systems.

Trickling bio-filters can be used indoor or outside.

Trickling bio-filters can be used indoor or outside.

14.  They enable higher stocking densities – particularly when coupled with solids removal devices.

15.  They enable the integration of a wider range of growing systems – aquaponic or soil-based.

Given the advantages that they offer (and in the absence of any good reason for not having them), I strongly recommend that they be a feature of any aquaponics system.