Thank you for your article, it has been a great ease to my puzzled mind on the types of bacteria and its abilities on the filter types.

One thing i’d like to ask is how do the Nitrobacter get into the canister bio-filter media? or has it been in normal tap-water all along?

For me i’ve been using holland sand as bedding for my aquarium with under gravel filter run by a powerhead. As well as a canister filter.

So to describe the effect, the nitrosomonas are actually living on the holland sand bedding converting ammonia to nitrite and taking up oxygen from the oxygenated water (its source from any nearby airstone providing the oxygen?)
After of which the Nitrobacters on the holland sand also break the nitrite to nitrate.

Then the nitrate is free floating in the water and eventually gets sucked into the canister where the bio-media filter, within containing the nitrobacter are very constrained of oxygen and rely on breaking down the nitrate for oxygen to survive. Which then the nitrate broken into nitrogen gas which exits the canister filter is released back into the aquarium and then goes upwards (since its so light) and goes out of the aquarium.

Would that be correct?

I believe that some aquarists still use undergravel filtration though they are very much in the minority.

The following is my opinion only. Using canister filters for bio support has drawbacks, the main one is nitrate. If the canister is well maintained, that is, there is sufficient mechanical filtration to protect the bio media and the mechanical area is cleaned regularly, the canister will give little trouble.

The undergravel filter has bacteria which rely on oxygen, as does the canister. It is necessary with both to ensure good seawater gas exchange to ensure a high ongoing oxygen presence.

The canister can be easily serviced. However the undergravel cannot. Having the seawater constantly drawn down through the sand inevitably draws in detritus, and the sand becomes very dirty. This can slow down water flow etc. The only way to deal with this is to clean the sand. Removing it and washing it with tap water kills all the bacteria. Washing it gently in seawater is better but what a slow and tedious job to rmove the sand from the aquarium! And will it be clean?

It is better to use a properly sized canister filter on its own, containing a sufficient amount of a good bio media (such as sintered glass) which in turn is protected by adequate mechanical filtration. As said, properly maintained there should not be a problem.

Having said all that, if there is sufficient live rock of good enough quality then the need for a bio canister filter should not arise. The canister filter could be used for pure mechanical filtration.