Biological filtration - high or low flow?

[chrisf]

I am about to set up a large new tank. It comes with a large exernal canister filter. I also have an old spare external filter which I am thinking of adding in to double up the filtration capacity, but only using the one motor.

Doint this would lower the flow rate through the filter due to the extra resistance.

So the question is this...

Is it better to have high flow through a small biological filter or a slower flow through a larger filter mass????

Chris

[FishLover]

You need to push the full tank water through the filter at least 3 times per hour. Less than that you are not going to get much from the bio filters no mater how much filter mass you put in there.

[fishgeek]

total ammonia nitrogen utilisation has some complex calculations

flow rate is only partly important - it is what brings the waste products to the bacterial colonies and also the other needed inputs for bacterial oxidation of ammonia (including most importantly oxygen)

but it also can take untouched ammonia right through the filter if traveling to fast

bacterial colony size also has a bearing on oxidation levels so surface area and filter volume are also important

i remember reading some good articles on estimating nitrogen utilisation through filters when designing my first little system
there should be more about it on line if you are interested

andrew