Biological filters, used in conjunction with effective mechanical filters, are the means by which people like you and I are able to grow our own fish. In short……no bio-filtration; no aquaponics!
Biofilters 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.
Some aquaponicists rely on the grow bed media…or the wet surfaces in their raft systems…to provide biofiltration but I highly recommend dedicated units.
Dedicated biofilters will make any aquaponics system more resilient and more productive. 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.
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 insertion of a dedicated biofilter 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.
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.
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.
Biofilters come in various forms but my personal favourites are the humble (inexpensive) trickling biofilter – or the more sophisticated (and more effective) moving bed bioreactor.
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.