What is happening in my pond in spring?

Springtime presents us with the perfect opportunity for checking the condition that winter may have left our pond in and to look forward to the summer by carrying out any necessary maintenance, nurturing our koi out of their winter slumber.

As a pond leaves the perils of the winter behind in preference to the ‘green shoots’ of spring, it undergoes a period of rapid transformation, especially if it is planted. The fish and pond have had the rest that nature intended and now is the time to ready the pond so it can navigate its way through this in-between period of aquatic no-mans-land – namely early spring. A risky period for koi and an important time to support them as required so they can make the seamless transition from winter inactivity to summer growth and vitality.

Recognising that koi are slaves to their environment, and that pond conditions determine a koi’s metabolic rate and behaviour, it is vital that we use this last opportunity to set the stage for the coming growth season.

What is happening to a pond in springtime?

It is helpful to take a koi’s-eye-view of a pond’s environment when assessing what effects specific water characteristics may have on a koi’s physiology. By doing so, before we look at what is happening to their pond in springtime, we should also look at what they’ve experienced through the preceding winter months.

Before rolling up your sleeves and getting stuck in to your pond, test your pond water while the koi are still not actively feeding, as this will help you set your agenda for pond maintenance and give you some indication as to how the winter went.

Two key parameters to test are pH and nitrate (as you would expect ammonia and nitrite to be zero with your koi not be feeding over winter). The pH can have a tendency to drop close to 7 over winter through the diluting effect of several months of rain and snow. As koi prefer a higher pH of around 8, topping up the pond with treated tapwater or adding a source of calcium carbonate will soon restore the correct pH.

Nitrate levels too are likely to have risen over the winter period because months of breakdown of organic matter and the products of fish metabolism (all be it very slow) are likely to have led to an accumulation of nitrates. If the nitrate level has risen to above 50ppm, then carry out a water change with water of a lower nitrate concentration.

Perfectly clear?

Your pond’s water will be at its clearest over winter and early springtime because the short days and cold temperatures will have prevented algae from growing. Furthermore, if you opted to reduce or even turn off the flow rate in your pond over winter, any suspended debris will have had the chance to settle.

However, spring is the season of lengthening days and warmer weather and your impressive clarity may deteriorate in a matter of weeks. Any accumulation of nutrients, coupled with increased sunlight and warmer weather is a recipe for nuisance-algae, whether green water or blanketweed. Furthermore, if a fine covering of silt has settled on your pond bottom, the combination of increased koi activity and pond turnover is likely to stir it up, spoiling your pond’s appearance.

Now is the time to act. When the pond’s temperature is below 10oC, fish are still inactive and you are able to see the pond’s bottom. Use a pond-vac (either buy or hire from your aquatic store) to meticulously remove the settled silt from the pond bottom. If silt remains on the bottom into the summer, this will act as a source of nutrients throughout the season, fuelling algae growth for months.

Once the water temperature rises consistently above 10oC, changes really start to take place and there is no looking back. It is important to use this sub-10oC window of opportunity wisely, getting the pond right (both aesthetically and biologically) so that your koi will also be right for the oncoming season.

How do changes in koi activity in spring affect your pond?

Imagine the 8-10oC temperature range as starting gate. As soon as koi pass through this, their activity changes and so does the character of the pond- hopefully for the better- but sometimes for the worse.

As soon as the water temperature rises above 10oC, koi naturally become more inquisitive and active as their metabolic rates increase, demanding more food to service their energy requirements.

The beneficial bacteria that feed off ammonia, nitrite and organic wastes produced by koi also become more active as the temperature starts to rise. They require a food source and a beneficial temperature for them to multiply and recolonise the pond and filter to a stage that they can keep on top of the task of processing all of the waste that the pond produces. If these wastes (that are directly attributable to the quantity of food entering the pond) are allowed to overrun the bacteria’s limited ability to break them down, they will accumulate to a level where they become toxic to fish and hazardous to their health. Another potential hazard for koi at this time that already poses many risks for their well-being.

An effective way of breaking in the pond’s bacteria while adequately meeting the koi’s increasing yet limited energy requirements is to offer them a low protein diet. Consequently, the koi consume and digest the majority of the food offered efficiently, keeping waste production to a minimum, helping to maintain a stable pond environment.

As koi rise out of their slumber, so too will pathogenic bacteria, parasites, viruses and fungi. These opportunistic organisms will have survived the barren winter conditions in low numbers, multiplying rapidly under the favourable conditions of a rising temperature and weakened koi. When your koi start feeding and coming to the surface, it is a good opportunity to have a close look at each of your fish. As each koi is unique, each will have over-wintered to a different degree. Most will emerge intact and in good condition, while others may have large external parasites attached or may have developed sores or ulcers, attributable to them by sitting on the pond bottom. Other common symptoms include fin or tail erosion or wax-like growths caused by a koi pox virus – a springtime phenomenon.

Being aware of the heightened threat from disease during these ‘in between’ temperatures, we can add a broad-spectrum treatment (usually a formalin and malachite green-based solution) to reduce the density of these disease-causing organisms. A repeated dose at the correct temperature can prove to be very supportive to your fish until their immune system becomes more effective in warmer temperatures. For the rest of the year, healthy koi are well able to protect themselves from disease.

How to keep your koi pond healthy in spring.

Keeping the pond healthy is the secret behind keeping your koi healthy, and in spring when things can change so rapidly, the emphasis is placed on keeping a check and control on that change so that things do not get out of hand.

The water.

Keep a record of the water temperature to check when it rises consistently above the magic 8-10oC threshold. Be sure to carry out major maintenance before this temperature is reached. As your koi will increasingly demand and digest food above this temperature, keep a regular check on the water quality, particularly ammonia and nitrite.

The Koi.

Each of your koi should rise out of their slumber and show interest in the food you offer. Watch out for any koi that remain huddled and disinterested on the pond bottom. Manually check the condition of each fish by netting and bowling them individually. Even though the temptation is great, resist from feeding your koi too generously as this will ultimately affect the water quality. For the first few weeks of feeding, only offer food in conjunction with water testing. Only continue to feed if ammonia and nitrite readings are zero.

What jobs need to be done in springtime?

Test your pond water. This will give you an indication of the state of your pond after its seasonal break. Test specifically for pH and nitrate.

Change the UV bulb. Unlike a biofilter where the media will remain and be effective for many years, the UV bulb must be replaced each year to keep green water controlled. Spring time is the most logical time to replace the bulb as it’s hardest work will be in the first 4 or 5 months of the season. Even if your current bulb appears to illuminate, its output will have deteriorated from last season, making it less effective against green water. Fit a new bulb now and you can forget about it for another 12 months.

Filter. If your filter has been turned off or even turned down over winter, it will have accumulated a good degree of solid matter. Springtime (sub-10oC) is a superb opportunity to carry out major maintenance as you are able to get away without upsetting its function (unlike summer filter maintenance).

If you have a friend who has been running a heated pond and filter over winter, ask if you can borrow some of their filter extract. This will contain a good cross section of autotrophic and heterotrophic bacteria (as well as other beneficial micro-organisms) and give your filter performance a real boost.

4. Now is the window of opportunity to remove any settled debris or silt from the pond bottom. Act before the pond’s turnover and fish activity increases, mixing the sediment. Rather than using a fine mesh hand-net that will do a good job a stirring up the silt, use a pond-vac.

Did you know that we offer koi a low protein diet in spring (and autumn) for the pond’s health just as much as the koi’s. Koi could quite easily be offered a high protein food in spring as it would not do them any harm, however, the elevated levels of waste produced from feeding such a rich diet would soon lead to a water quality problem – and a koi health problem. We feed koi a lower protein diet because it is better for the fish and the filter.

Danger Signs.

Koi emerge in spring with imperfections/sores on their body, or damaged extremities to fins and tail. These symptoms must be treated topically, backed up by a pond treatment regime.

Individual koi showing abnormal behavioural signs. Bowl these koi and check for any obvious external lesions, remembering to check the underside of the koi. Treat accordingly.

Watch out for ammonia and nitrite levels rising, as early feeding can soon overburden a seasonally immature filter. Feed and monitor water quality in tandem and educate the filter to progressively handle more waste.

Kill blanketweed and string algae.