The bacteria serves to turn the deadly Ammonia into Nitrites, and this will allow the bacteria to flourish and
breed. ( Because this is processing the Ammonia it will cause the Ammonium to break up back into Ammonia
and H+ to be processed) Ammonia levels in the aquarium go down, the number of bacteria stabilizes and
voila, your tank is cycled, ready to have fish and work through more ammonia.
Hang on a sec… I mentioned Nitrites, guess what, they are also toxic to your fish, I lied, your tank isn’t
cycled. A second set of bacteria have to be established and will process the Nitrites by further oxidation into
Nitrates. This bacteria like the original one will breed on all the hard porous surfaces of your tank.
Hard porous surfaces, some people like to think is a euphemism for filters. Whilst not wrong, it can also be
the minute and miniscule pores on your gravel, the biofilm that forms on your rocks, the nooks and crannies of
the microscopic nature that form on your driftwood, the surface of your plants even the bodies of your fish.
Even without a filter, (which I wouldn’t attempt unless you were an expert), the bacteria will breed and multiply.
So we are left with these nitrates. Guess what, nitrates are non toxic! YAY! Sort of… Not really… No they
really aren’t. Nitrates like all waste in the aquarium can build up to toxic levels and kill your fish. This is why we
perform water changes. This is why people advocate the use of plants.
This is also where bioload comes in, if you have too many fish/too much waste breaking down/ or even too
many pooping snails, the bacteria wont be able to keep up with the load, there simply isn’t enough of them and
your tank will quickly become an ammonia laden cess pit.
Before I continue, I would like to add, Nitrates are an excellent source of food for plants, they help the plant
grow and provide a good way to remove the Nitrates from the water column.
Plants also will process Ammonia directly, so in conjunction with bacteria, will form an Ammonia
fighting super team.
3. Oxygen and Carbon Dioxide
So far we have learnt that Carbon Dioxide will cause an aquarium to become acidic and that plants process it
to form HCO3-. This is true. Plants however, also break up Carbon Dioxide molecules through a process
known as Photosynthesis. This basically means that a plant will use energy from the sun (or the micro suns we
like to call CFL’s, Fluoros, LED’s etc), to break up CO2 into C and O2. This is beneficial for both the plants and
the fish. The CO2 is toxic to fish at high concentrations. O2 is essential for life, this seems a pretty good trade
off. It gets better though, the plants use the C (Carbon) that they have just scrubbed out of your water as a
building block for their growth. The energy they get from photosynthesis allows them to develop Glucose and
Cellulose Polymers out of the Carbon and to grow and make your aquarium beautiful.
Bioload features here as well, if the bioload on your tank is too high, the plants (or atmosphere in an
unplanted tank) wont be able to keep up enough dissolved oxygen for your fish to be happy and they will
slowly but surely get ill and die.
Also, plants at night time as I mentioned earlier no longer photosynthesise, instead the release CO2, just like
fish and take in oxygen. Major problem if your tank is overstocked. Major problem if your tank is poorly
buffered and can’t stand the PH changes due to the increase in CO2 concentrations.