For the water gardener the coming of spring seldom fails to arouse feelings of enthusiastic expectation and excitement as the prospect of another period of renewal and aquatic activity approaches. As temperatures begin to climb and the period of daylight lengthens, the whole pond begins to stir, slowly awakening from its winter slumber in direct response to the certainty of the gradually changing season. With new growth sprouting from the dilapidated remnants of last year’s prunings, marginal and deep water plants begin to take on a different form. Fish, for the most part unseen during the cold winter months, start to visit the surface again with increasing frequency as appetite becomes stimulated by the warmer conditions - their interval of dormancy at an end. Now is the time for taking stock, planning any future changes and for undertaking a general ‘spring clean’ so that the pond and surrounding area will be in optimum condition for those all important long hot summer days to come.

Eco-pressures: It is also necessary at this time to pay attention to water quality, for during this period of regeneration various hidden pressures may be exerted upon delicately balanced system that is your pond, which can result in apparently unexplained fish losses at a time of year when such fatalities might be least expected. If things are in need of a bit of a clean-up but not a total spring clean, a general clean and tidy up in and around the pond with perhaps a 10% water change to freshen things up, could make all the difference. In circumstances where water quality is found to be unsatisfactory a greater percentage of water may need to be replaced - but more about this later! Carefully remove from the pond any previously unnoticed debris such as leaves or twigs, as these constitute a pollution threat. Also try to take out any accumulations of blanket weed as they occur, since these can have important indirect implications on the stability a quality of your pond water

Water quality:  Water is clearly the vital ingredient; the life support system of your fish. Its quality must of course be considered of paramount importance at anytime - but none more so than now as the pond and all its biological processes begin to speed up. It is highly desirable therefore, that you are aware of what is going on by testing for certain pollutants so that where problems exist action can be taken before serious damage occurs. Inexpensive and easy to use kits are readily available for this purpose from all good koi stores that will enable you to accurately monitor your water for the presence of these contaminates as well as for determining fluctuations in the pH (acidity/alkalinity) level of your pond.

All fish excrete into the water waste matter in the form of ammonia, a highly toxic substance.  This must then be broken down by organisms into nitrites and eventually less harmful nitrates in a natural process known as the nitrogen cycle. These friendly bacteria are active in the lilt layer on the bottom of the natural ponds and on the media and mechanical parts of essential filtration systems. Providing that the pond system is maintaining a reasonable balance, few difficulties should be experienced, the nitrifying bacteria well able to cope with the quantity of ammonia being produced. It is only when this equilibrium is upset that problems start to occur and there are many factors that can influence it - overstocking and overfeeding being among the most likely.

Boosting reserves:  During the winter months everything in the pond has been in a state of semi-hibernation, fish will have consumed very little while existing on body reserves built up through the previous summer. Consequently only relatively small quantities of ammonia will have been excreted into the water during that time. Now with temperatures rising, fish metabolism increasing and appetite returning, the system is suddenly put under pressure - unfortunately it may not yet be in a position to cope!

There is, among some pond keepers, an understandable, though totally misguided, belief that as fish emerge from winter dormancy it is necessary to introduce large amounts of food to compensate for the previous months of fasting. This is an extremely dangerous practice since the resultant surge of ammonia waste entering the water can overburden and pollute the system before the essential bacteria colonies have had a chance to become properly established. Remember that a biological filter switched on today will take some six weeks to become fully effective. Instead, feed only very small quantities of easily digestible food to start with, increasing gradually as the weeks pass and the water temperature rises. At no time should fish be overfed; little and often is by far the best and healthiest feeding strategy.

Never forget that fish out of necessity pollute their own environment - the more they eat the greater the pollution, it really is as simple as that. The actual toxicity of a given quantity of ammonia waste in a body of water does not necessarily remain static. It is influenced quite considerably by the pH of the water as well as temperature. Alkaline water in conjunct with a rising temperature, for instance, will make ammonia far less injurious to fish than when present in more acidic conditions. Generally speaking, pond fish are pretty hardy creatures and can tolerate a wide range of situations provided that changes take place gradually. It is when sudden swings occur that problems often start and at this time of year as everything is beginning to speed up, the potential for such fluctuation is perhaps at its greatest.

To measure the level of acidity/alkalinity, chemist have set up a recognized scale by which its intensity can be easily expressed. The term used is pH and it runs from 0-14. PH0 at one extreme is pure acid, while pH 14 (pure alkali) is at the other. Where acid and alkali are present in exactly equal proportions the reading would be a pH7, termed neutral. The important thing to remember when considering variations in pH is that the scale is set logarithmically which means there is actually a tenfold difference between full numbers. For example, a reading of pH6 against one of pH7 shows a change in acidity by a factor of 10 (x10), whereas a reading of pH5 against one of pH7 indicates a change by factor of 100 (x100).

Toxic effect:  It will be realized therefore, that even an apparently small variation on the scale can indicate a significant increase or decrease in overall acidity/alkalinity of the water and thus possibly influence the toxic effect of any ammonia present upon the fish in the pond. The pH of your water as it comes raw from the tap will vary greatly depending upon the area of the country in which you live. The nature and geology of the landscape upon which it falls as rain will determine its eventual acidity/alkalinity, in much the same way as general water hardness/softness varies considerably from region to region.

So from the point of view of ammonia toxicity toleration, some pond keepers may theoretically be more fortunate than others. However, in practice, the only really safe level of ammonia is absolutely zero. In the spring, algae and blanketweed start to flourish as the pond temperature rises and daylight lengthens and intensifies. This can cause the pH of your water to fluctuate sharply upwards as the day progresses through the natural process of photosynthesis. In extreme cases the difference between a pH reading taken from the pond in the morning and one in the afternoon can be quite dramatic. With a biological filtration system perhaps not yet fully ‘on song’, and increased fish feeding taking place all the time, ammonia concentrates in the water can quickly reach dangerous levels. If this situation coincides with a high pH alkalinity reading, lessening even further the fish’s tolerance to the pollutant, fatal consequences can result, with the larger specimens likely to succumb first and die.

Undesirable elements:  Before you panic, it should be appreciated that in many respects this represents the very worst that can happen. It is intended only to draw attention to the way in which undesirable elements can come together in certain circumstances to produce serious or distressing problems. Nevertheless, it does serve to emphasize the need to monitor water quality carefully, particularly during this fast changing season. Thus where fluctuating conditions or pollutant build-up occurs, action can be taken before too much harm is done.

Where serious water quality imbalances are detected the most effective way of bringing rapid relief to the system is a partial water change. Stop feeding, remove up to 40% of the water (depending upon the severity of the problem) and replace with fresh tapwater together with dechlorinating and conditioning agent. Continue to test and monitor until water quality is back under control.