Allotment Articles 2.
How A Filter Works
When a filter is first set running, whether it is in a tank or a fish pond it will simply be a physical filter for its first few weeks of operation. This is because it takes 8-10 weeks of constant running for a sufficiently large enough colony of nitrifying bacteria to establish itself to do the job properly of purifying the water. Adding bacteria in solution can speed up the whole process, or even adding freeze-dried bacteria will start the colony off.
Nitrifying bacteria are aerobic, that is to say they live in highly oxygenated water feeding off the ammonia in the water. That is why it is essential to keep the pump running continuously.
Nitrogen compounds are poisonous to fish as can be seen by the fact that when farmers spread fertilizers on their fields and it rains washing them into the canals and rivers, the fish die. Nitrates are to be found in fish wastes along with ammonia that is also very toxic. Inside a filter, different types of bacteria break the ammonia down into nitrite and then nitrate, (which is a less harmful and more stable compound) and then eventually into nitrogen gas.
If a filter isnít working properly, you can soon tell without even testing the water, because where the water reenters the pond you will see white bubbles. This is ammonia being oxidised to form a white scummy solid.
If this happens do a partial water change immediately. If in any doubt about the nitrite, or nitrate levels then simple test kits are available. It is probably worth keeping an eye on the PH levels as well because this can swing wildly if the filter isnít working properly. A PH reading of 7-8 is fine, 7 being that of neutral tap water.
As a filter matures small water creatures will also establish themselves in the filter. These will help break down the larger particles of matter into a chemical solution that will again be neutralized by the bacteria. If the filter should be turned off for any length of time, such as when the pump breaks, or for the duration of winter, then the aerobic nitrifying bacteria will die and anaerobic bacteria will flourish. These produce a poisonous waste that may kill the fish when the filter is turned back on again. So the filter should be washed thoroughly before starting it up again and it should be treated like a new filter.