Simple nitrogen cycle | biofilter media & the nitrification process
Biological Pond Filters & The Nitrogen Cycle, Ensure Clean Fish Ponds
In order for the simple nitrogen cycle to take place in your biological pond filter naturally occurring ammonia oxidizing bacteria need to be present on the biofilter media housed in the filter chamber. The higher the SSA (specific surface area) of the pond filter media the better as this ensures higher numbers of beneficial bacteria to carry out the process. A regular supply of nitrogen in the form of ammonia is required (provided by koi and other pond fish solid and liquid waste). A regular supply of oxygen is critical for the nitrification process to take place; normally provided in a garden pond environment by an air bubbler, water fall, fountain, fountain spitter or oxygenating plants.
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How does the simple nitrogen cycle take place in pond filter systems?
Your new liner pond has been built and filled and you have installed the following pieces of pond keeping equipment into the system: biofilter, pond pump, UV sterilizer (UV clarifier), air bubbler, waterfall and a pond skimmer. You have also placed a few low cost goldfish into your pond.
The biological pond filter needs to bed in and reach maturity. This is where the goldfish come into play. As they release ammonia into the pond water Nitrosomonas and Nitrobacter nitrifying bacteria will appear and start to colonize the biomedia within the pond filter. These beneficial bacteria feed on nitrogen, found in ammonia, under the influence of oxygen. As soon as the goldfish are fed they secrete small amounts of ammonia into the pond water.
Nitrification process - Stage 1: An 'ammonia powered' bacteria known as Nitrosomonas converts ammonia to Nitrite (NO2) which is less harmful than ammonia but will still poison your fish if sufficient quantities remain in the pond environment. On average your fish are capable of withstanding twice the level of nitrite in the water than ammonia (based on same volume of pond water). Nitrosomonas starts to feed on the ammonia, converting it into nitrite. It takes approximately 18 hours for the population of Nitrosomonas to double. At this initial stage the level of ammonia will continue to rise at a faster rate than it can be removed because the biomass (size of bacteria colony) is still small.
The following occurs as Nitrosomonas converts ammonia into nitrite: ammonium (NH4) + oxygen (O2) produces nitrite (NO2) + 4 lots of hydrogen. Over a period of about 10 days you will notice a drop in the level of ammonia in the pond and an increase in the level of nitrite. A further 10 days on and the level of ammonia has dropped dramatically. After approximately 40 days, ammonia levels will be negligible. In the meantime fish are still excreting ammonia and the level of nitrogen in the form is growing; some as ammonia and some as nitrite.
Nitrification process - Stage 2: Bacteria known as Nitrobacter convert the nitrite produced during stage 1 into nitrates. Nitrates will remain in your garden fish pond indefinitely, unless there are pond plants present that use the nitrates as a valuable source of nutrients. Aquatic pond plants use up the nitrogen part of the nitrate to aid their growth. Two portions of Nitrite (2NO2) + oxygen (O2) produces 2 lots of nitrate (2NO3). At around day 40 after kick starting your system the levels of both ammonia and nitrite are negligible. Your filter has now reached maturity and can pretty much convert ammonia into nitrate quickly.
Great everything seems to be working just fine! You now add a few more fish and guess what? That's right the level of ammonia starts to increase. The secret is to gradually introduce new fish over a period of time, to avoid ammonia levels hitting the roof because you have placed to much strain on the biofilter.
How Do I Increase My Biofilter Performance?
The first thing to do is to try to reduce the load placed upon your filter. A good way of doing this is to only feed your Koi and goldfish high quality branded fish food, with a low ash content and a high proteins content. Ensure that trace elements, vitamins and minerals are also present.
Hopefully you will realize that a large surface area on which nitrifying bacteria can live is a good idea. The larger the surface area for them to live on, the larger the size of the colony. The larger the size of the colony, the quicker ammonia can be converted. If you are using a pressurized pond filter model such as the Oase Filtoclear or Hozelock Bioforce range then replace the pond filter media gradually over a period of time with Supra biomedia. Trust me, you won't regret it! The Fishmate pressurized pond filter range comes as stand with Supra, low cost, high surface area bio media.
Note: The beneficial bacteria in your koi pond biological filter chamber need a constant supply of oxygen (24/7/365) for the nitrogen cycle to take place. If oxygen isn't available then within several hours the beneficial bacteria will die resulting in ammonia levels increasing. Always provide your pond system with as much oxygen as possible, whether that be from a pond air pump, waterfall, fountain or some other method. It really is that important.
Many commercially sold pond filters are supplied as combo units, that include both a UV sterilizer and a biological filter. The reason being twofold: firstly a financial one in most cases and secondly because of the ease of installation. Larger koi ponds on the other hand will require Professional Biofilters due to the volumes of water and the levels of koi.
It is important to understand that the UV sterilizer (UV clarifier) plays it's part in the water purifying process by removing / preventing green water. It is important to Manage Algae Bloom (green water) because too much will starve the pond of oxygen and suffocate your koi and goldfish.
Oh by the way in case I forgot to mention it? The Nitrogen Cycle or Nitrification process is so called because Nitrogen is continuously recycled. It enters the system in the form of fish food, actually proteins, which are consumed by your pond fish, which in turn excrete ammonia into the pond. The ammonia is broken down into Nitrate which is eventually consumed by plants who release Nitrogen back into the atmosphere.
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