Pond filter in spring

Our gardens, and everything in them cannot avoid the seasonal variations in temperature – responding accordingly with periods of inactivity and growth in winter and summer respectively. As spring approaches, life within our garden and koi pond is not be able to resist nature’s call to awaken, grow and thrive. Just as we will have to bring our lawn mower out of semi-retirement as the grass starts to grow, so too will our pond need to be rejuvenated, especially the filter which is charged with the responsibility of maintaining the health and life of our pond and the fish that swim within it.

In the same way that our lawn mower will benefit from a few pre-flight checks having been out of service for several months, so too will our filter, especially if we haven’t given it much consideration over the winter period. Your filter should be treated with great respect at all times, but especially during this period of limbo between winter and spring. Get things right now, and your fish will be able to slip back into their feeding and growth phase without any problem.

How has your filter overwintered?

There are three strategies of overwintering a filter. The amount of effort required to kick-start your filter this spring will depend on how it has been overwintered.

1. Heated ponds. If you have heated your pond over winter, and have continued to feed your koi and maintain your filter no differently to summer practices then your filter will not require a kick-start this spring. Ensure that the transition in temperatures is kept as smooth as possible, so that ambient temperature seamlessly takes over when the heater is turned off.

2. Continuous filtration at ambient temperature. If you have opted to run your filter at ambient temperature through the winter, then your filter may require a spring clean, especially if you have not maintained the pond and filter throughout winter.

3. Filter turned off over winter. Many koi keepers choose to turn off their filtration completely over winter, recognising that there is little demand for filtration when koi are completely inactive. It can also help to keep pond water from being chilled and can save on the running costs of a pump. Depending on how this filter is maintained over winter will determine how much kick-starting is required. If it is a trickle-fed, gravity-return type, then it is likely to have drained dry overwinter making it more difficult to kick-start. If however, the media has been allowed to stand in water as in a gravity-fed filter, then this will be easier to kick-start.

Why do filters require a spring kick-start?

The key objective behind any pre-spring-clean of a filter is to reduce the risk of a New Filter Syndrome type catastrophe. In many respects, a filter that has lay dormant or has been inactive for several months will quite naturally take time to respond to the sudden increase in ammonia the results from the onset of feeding. Factors such as the near-freezing water temperatures, the lack of ammonia and in cases where a filter may have been allowed to dry out, the less than ideal environment, will all combine to reduce the filter’s performance when it is called to action in the spring. However, we must remember that it is quite natural for the number of filter bacteria and associated micro-organisms to decline over winter as a result of the inhospitable conditions, just as it is quite natural for the surviving population of filter bacteria to repopulate the filter as the supportive pond conditions of spring arrive. What is not natural, is the rate at which ammonia is produced by the high-density of koi in a koi pond quite literally overnight in the first days of spring, having been offered no food for months and then handfuls of food overnight. Just as this style of feeding should be avoided in a new pond and filter system, so too must it be in a pond in early spring. Especially as the pond is already fully stocked – something that is not the case when running in a new pond and filter for the first time. So the filter must be kick-started to prevent a phenomenon akin to NFS (which we could call Spring Filter Syndrome – or SFS).

What is involved in the spring filter kick-start?

1. It is inevitable that a degree of solid organic matter and other debris will have collected in your biomedia. This will contain a good cross-section of autotrophic bacteria (responsible for breaking down ammonia and nitrite), heterotrophic bacteria (responsible for breaking down the organic matter) and other beneficial filter micro-organisms. However, settled debris will impede water flow and adhesion of bacteria to the large surface area of biomedia in your filter. It should be removed, but gradually so as to allow your filter to re-seed itself over the first weeks of spring. A good way of doing this is to clean the first two-thirds of your biomedia in pond water, leaving the last third untouched for several weeks after you have recommenced feeding your koi. This will prevent you from completely removing the beneficial diversity of micro-organisms, while clearing up the majority of surface area for recolonisation.

2.This of course must be done at the same time as an extensive clear-out of the mechanical function of your filter. The mechanical chambers/ areas of your filter can be cleaned thoroughly until no debris remains. This may involve replacing any worn-out mechanical media. It is this media that will prevent your newly cleaned biomedia from blocking up again with silt.

3. To assist the recolonisation in those filters that may have been left to dry out over winter, you should consider using a bacterial filter start solution. Even in a dried-out filter, there will be a degree of beneficial residual life that should be retained. Wash out two-thirds of the biomedia in pond water, and as a boost, add the filter bacteria. It is important not over clean even dried out filter media as they will hold a far greater array of beneficial microbes then a filter start solution. These bottled kick-starting solutions only generally aid the ammonia and nitrite function of the filter. Held within your dirty media you will have a diversity of microbes that are typical of a mature by a filter and should be used and conserved at all costs.

What will have been happening in a filter over the winter months?

Assuming the filter is handling recirculating pond water at ambient temperature, the filter is not required to perform a biological role, and in any case it is not able to. Ammonia production will be negligible from within the pond, and as the water temperature approaches 0 degrees C, bacteria responsible for breaking it down become inactive, being unable to function properly. Meanwhile, mechanically, a filter will continue to accumulate particulate matter, both in the preferred mechanical chamber but also, unfortunately within the biomedia. As rates of decomposition are much lower in winter there will be little biological remineralisation of such debris, causing it to accumulate and hinder future bio media function.

How will I know if I have kick-started my filter properly?

The signs you look for are the same as those when assessing whether a new filter is coping with the at the stock of koi and feeding regimes; these are the ammonia and nitrite levels. Ammonia and nitrite levels must be zero, and if either give a positive reading, this will show that your filter function is not managing to keep up with the rate at which ammonia and nitrite are being produced. In such circumstances, stop feeding until your ammonia and nitrite readings return to zero. In extreme cases you may have to carry out a diluting partial water change. You should feel your way over the first month or so of feeding in spring to ensure that your rejuvenated filter is able to cope with the sudden influx of ammonia. You can help this process by feeding a low protein (20%) diet – (Protein being the chief source of ammonia in a pond).

Don’t disturb your filter:

1. When it is brand new, and is starting to mature in a new pond. Don’t be tempted to tinker, but leave it alone and help mother nature take her course.

2. When you have a high nitrite. Leave your filter to battle on, but supported by a partial water change if necessary. Also – stop feeding.

3. All at once. Carry out filter maintenance in a piecemeal fashion to preserve some maturity and biodiversity and so to protect its function.

Kill blanketweed and string algae.