Can I avoid water pond problems from the start by having a biological filter?

The Mucky Mystery of Pond Sludge: Is it Necessary?

If you already have a pond with fish in, you might feel that you need a filter because your water is so green that you never see the fish. That might be your only reason. But it is not the reason you need the filter. The filter might enable you to see the fish, albeit for a short time, but you will not really have cured the cause of that green water. You have treated the 'headache', but not the cause of the 'headache' in the first place.

The green water is caused by millions of single celled plants called algae that thrive in sunlight and feed of the excess nutrients in the pond water.

In a pond or pool we hope to establish what is described as the Nitrogen cycle, in which the organic matter in a pond that is dead animals, bits of plant material and excrement, all gets broken down by bacteria to chemicals that are actually of some benefit to the pond environment. These are mainly taken up as nutrition by the plants (including algae if they get a look in).

The high protein from fish food if it is allowed to rot on the bottom of the pool, also with the natural metabolism of fish, particularly Koi carp, and the excrement of fish, all go to produce high concentrations of ammonia. This is highly toxic to fish, especially koi carp. Under normal circumstances, the ammonia is usually broken down by nitrosomona bacteria on the bottom of the pond to nitrites and then further by nitrobacter bacteria to nitrates - plant fertiliser. These bacteria need oxygen to survive and indeed the chemical process involves the linking up of the nitrogen atoms in the ammonia with more and more oxygen. We therefore go from Nh3 to NO2 to NO3.

If the pond is highly stocked with fish it will not only mean that the resources of oxygen are under pressure from the respiration demands of the fish, but also the chemical process of waste breakdown is creating oxygen demand. The trouble is that if the fish are under stress themselves from the overcrowded environment, let alone from the high level of toxins in the water, their metabolism increases and they themselves produce more ammonia directly from their gills. We therefore get a 'snowball effect' of pollutants.

The oxygenating plants in a pool are essential ingredients in the Nitrogen cycle. They use up the plant nutrients before the algae benefit from them, at the same time as returning oxygen to the water. But the oxygen will not stay around long enough to be appreciated if there is too much ammonia about. Also if your passion is for Koi then the life expectancy of any oxygenating weed growing in the pool is pretty limited anyway because they will gobble them up as they do virtually everything they can get in their mouths.

Therefore in all the gradations from a pool being slightly overstocked to one of a monstrous environment where even the toughest water weed doesn't even get a look in, having a biological filter is the best insurance you can have (particularly in hedging against the extremes of the climate). By having a biological filter, you are taking what would commonly be happening in the bottom of the pool and putting a fast moving force fed version on the side of the pool out of harms way and under your control. I call it a turbo version because you are feeding fresh oxygenated water containing organic debris to a bacteria culture that will flourish and perform with exceptional ability, just like a combustion engine fed with the right balance of petro-chemicals and air.

Because of this an external or poolside biological filter, in order to be effective, it must be run 24 HOURS A DAY; the constantly fresh supply of oxygenated water is what keeps the bacteria in the filter thriving. If they are deprived of this for even a couple of hours then they will start to die and the filter loses effectiveness.

What this filter also does is remove algae from the pond water as it passes through it, trapping it in the medium, allowing it to die and be digested by the population of bacteria. This avoids any excess loading on the balance of the pond from the dead and decomposing algae. This process is doubly effective in conjunction with the use of a 'U/V Clarifier', which "zaps" the algae before it enters the filter box.

Water chemistry

Without the aid of a water-testing kit, problems with water chemistry are seen manifested in problems with algae (green water, cotton wool growths of blanket weed), fish health problems or fish behaviour problems. In fact most experts in fish keeping propound that the susceptibility of fish to all pests and diseases is directly related to the quality of their environment i.e. the water they live in. Therefore in looking for a permanent cure to any fish ailments then the answer lies in intelligent water management.