Build your own active bed bio media chamber to suit your needs

Active bed bio media is a versatile biological filtration medium. It is easy to encompass in just about any filtration situation where conventional static bio media is being used. From Koi ponds to marine aquariums to home waste water treatment systems active bed bio media has a wide variety of roles it can be used in.

Active bed bio media works be being moved around in water by air bubbles. Because it has a specific gravity very close to that of water (active bed bio media is very slightly buoyant in water) this movement is easy to achieve. All that you need to have is a chamber that is not pressurised and an air pump, and of course the active bed bio media.

How much active bed bio media do I need?

Active bed bio media is very efficient owing to its moving bed process. Other media such as porous volcanic rock can have many times the surface area of active bed bio media per cubic metre but because these media are static the active surface area is in fact greatly reduced because the water merely flows over the fine pores, and you also get a reduction in efficiency as water tends to channel itself through the paths of least resistance.

Active bed bio media is thus rated by load of ammonia and a good rule of thumb is to cater for a 50l bag of active bed bio media per 250 g of HIGH quality Koi food fed per day. This is a conservative rating for active bed bio media but when it comes to our precious Koi it is the one we use!

The other factor that determines how much active bed bio media you need is the size of the chamber you wish to put the active bed bio media into.

Active bed bio media operates at best efficiency when it is at between 30 and 70% density by volume in a well agitated chamber. This means that if your chamber is 100 litres in total size, you can add one bag of active bed bio media to this for a 50% by volume density ratio.

If your chamber is 300 litres in capacity you will need two bags of active bed bio media (a total of 100 litres) which will give you 33.3% density by volume. The great thing about active bed bio media is that if you need extra filtration capacity all you do is add another bag or two. In the case of a 300 litre chamber you can add another two bags to give yourself double the capacity and your active bed bio media operating at a 66.6% density by volume.

In terms of selecting an airpump to handle the task of creating the air bubbles required to move the active bed bio media bed a rule of thumb is that you will need 15 litres of air per minute per bag of active bed bio media. Thus a Happy Koi 40 air pump is perfect for driving a chamber containing 2 or 3 bags of active bed bio media if it pumps air through airstones at 60 to 80 cm depth.

Determining how much active bed bio media you will need when considering your pond size is a little more tricky.

If your pond size is say, 15 000 litres and you stick to the rule of one Koi per 1000 litres you will end up with 15 Koi in the pond. When they are small and weigh 200 to 300 grams each, the total fish mass in the pond will be 4.5 kg approximately. If you feed heavily at 2% of body mass per day you will end up with a feed rate of 90g per day, which is well within the capacity of a single bag of active bed bio media.

When your fish are at their largest size, and let's assume they all make it to the magical 80 cm mark (80 cm is a huge fish with only the exception growing beyond this), you will have 15 fish all weighing in about 12 kg each which gives you a total fish mass of 180 kg. Again feeding these size fish heavily at say 1.0% of body mass per day (which is far more than they will ever eat but for purposes of illustration) you will be feeding 1.8 kg of food a day. Given that each bag of active bed bio media can handle 250g of food per day you would need 7 bags to do the job.

This is of course extreme. Feeding nearly 2 kg of fish food a day  to 15 big fish is way over the mark. However, with Koi it is always better to over spec your filter requirements operating on a worst case scenario. Catering for this scenario doesn't mean you have to add all the active bed bio media from the word go, but that you should cater for being able to add to this theoretical requirement should it become necessary.

Active bed bio media and loading

Practical experience has shown that active bed bio media does better when shielded from direct sunlight. The bacterial colonies that we seek to cultivate on the media are better off in low light or no light conditions.

You can really load your active bed bio media once it is mature. We have found that active bed bio media is virtually bomb proof once it has started going a light brown colour. The colour is an indication of the maturity of the media and of the number of bacterial colonies forming on the media. Ideally the browner the better.

However if you have more then enough active bed bio media for the task at hand the bacterial colonies merely 'tick over' when reducing the relatively light ammonia loads. They thus take considerably longer to go brown. A light brown colour is not an indication that the active bed bio media is not working but is rather an indication that the loading on the media is not yet high enough and that there is plenty of 'reserve capacity' in the media to cater for future expansion as your fish grow.