Growth kinetics of bacteria involved in nitrogen cycle in aquaria?

Question

What are the optimum growth rates of nitrosomonas/nitrobacter in aquaria ? Sometimes the water turns cloudy slowly and doesnt go away for weeks, why is this ?

Answer 1

I'm a fermentation scientist and I work with bacteria,
growth kinetics/phases, protein/plasmid DNA
production, genetic modification and interference with
metabolic pathways. So I realise my answer might be a
bit too long and complicated.

Bacteria commonly exhibit three phases of growth, a
lag phase, exponential phase and a stationary phase.

First the growth is slow and the growth rate is slow
as well (lag phase). Then the growth is exponential,
rapid and the growth rate is constant. Then the growth
rate starts to slow down until it becomes zero.

All three of these patterns can be observed perfectly
for a SINGLE strain of bacteria in a vessel with has a
limited starting concentration of nutrients and
constant temperature/pressure/light and in case of
aerobic bacteria, a high dissolved oxygen content.

Now to transfer this knowledge to an aquarium
situation. Lets look at the complication.

1. You have various species and strains of bacteria,
they have different growth kinetics and
characteristics and they compete/interact with each
other (The growth pattern of those that might rely
more on nitrites, will depend the activity of those
that metabolise ammonia into nitrites).

2. You are observing growth by the
turbidity(cloudiness) of water. If bacteria adhere to
surfaces they will continue to grow but you may see
the water as clear. Therefore the basis of measurement
if flawed, it may show less bacteria than what is
present.

3. Growth rate differs for different temperatures and
every nutrients affect growth patterns differently.

Therefore growth rate in aquariums is

a) different for every aquarium,
b) calculated inaccurately.
c) depended on many factors.

The bottomline is for nitrosomonas and nitrobacter is
that if you want growth rate you need to specify
temperature and nutrients in the aquariums, the latter
is impossible to describe chemically and reproduce
experimentally.

Lastly nitrosomonas(not sure about nitrobacter) are
soil resident. Different organisms have been suggested
as being involved in the nitrogen cycle in water. I
can't honestly remember the names at the moment, I'll
need to read into it and find out more.

Now the steady rate you observed might have been due
to low levels of certain nutrients present. And since
it persisted for such a long time, your filter
material did not "hold" the bacteria passing through
it. What I mean is that, when you first start the
filter, it's empty and slowly bacteria adhere to it
and live attached the filter surfaces and not
suspended in the water. Over time debris and dirt
accumilated providing more surfaces making the
"pores/holes" in the medium smaller and thus capuring
smaller particles (due to small pore size) and more
bacteria (due to larger area available for adhesion).
Therefore since you havent described what
filter/filter media you are using I cant suggest
anything specific but to say that you should
incorporate a finer filter material. 8 weeks is a
very long time. I suggest you check your filteration
system.

Answer 2

Lots of variables go into determining the population growth. Temperature is a big part of this, since warmer temperatures (at least to a point) increases their metabolism.

The availability of ammonia and nitrite (as an energy source) does as well. This is why fishless cycling works, you don't need to do water changes to protect the fish from ammonia and nitrite poisoning. Along those same lines, the frequency and amount of water removed during water changes if you have fish in the tank (and the amount of food used to feed them), whether or not a siphon is used to clean wastes and excess food from the substrate are all going to have an effect on how quickly or slowly the population grows.

So for the best bacterial growth, no fish, start with filter media or gravel from an established tank to seed the new one, adding an ammonia source, and turning up the heater to 85-90o, and no water changes will all decrease your cycling time.

Answer 3

If the cloud is white, it's a bacteria bloom (green or brown would be algae).
A tank is cycled normally in about 4 - 6 weeks. In my first tank the cloud lasted about a week...but the entire cycling process took less than 3 weeks. The other tanks didn't "bloom" but ran the whole 6 weeks to cycle. If you get a cloud, it should be a sign that it's cycling quickly. Of course, that can mean more stress to the fish than normal as well.
Do a lot of small (10 - 25%) water changes, don't clean decor, aquarium walls or the filter media and test, test, test to make sure your fish are okay.