Summer is the high-point in the water-gardener’s calendar – a time when the pond should be at its best and plants fish and wildlife thrive, bloom and breed; in short, summer is payback time for all the planning, planting and sheer effort involved in getting this far in the first place. At the same time, those long sunny days and hot, humid nights can bring challenges of their own for the unwary pond-keeper, so alongside the justifiable enjoyment of the fruits of our labours, we also need to keep an eye out for signs of trouble. The warmth means things can change very quickly in the pond and, if the early signs are missed, problems such as algal blooms and deteriorating water quality can soon become major summertime headaches. With a little bit of vigilance and a spot of careful summer maintenance, however, we should be able to avoid having our enjoyment spoiled too much.
Changes in the pond and the behaviour of its inhabitants during the warmer weather can make water quality problems more likely, principally in terms of dissolved oxygen and nitrogenous waste – both of which are particular nuisances for ponds stocked with fish.
Oxygen dissolves naturally in water, but how much oxygen water can hold depends, amongst other things, on temperature; in short, the warmer the water, the less dissolved oxygen (DO) it contains. This is, clearly, a potential problem during the summer, since low DO levels precisely coincide with the time when fish require the most oxygen. In a well stocked pond particularly, this may cause a problem for the inhabitants, especially if it is well planted. Although an adequately sized waterfall, cascade or fountain should ensure that sufficient is added to meet their needs, it is important to remember that while plants contribute abundant oxygen to the water during daylight, they themselves use it at night. A heavily planted pond – or one full of algae – can develop seriously depleted oxygen levels as dawn approaches, especially if the previous day was a very warm one.
Pond Air Pump
Installing a pond air pump with a diffuser stone – a giant version of the familiar aquarium set-up – can help, as can ensuring that at least half of the surface area of the pond is open to the air. Ponds covered in duckweed or fairy moss, for instance, tend to have little natural oxygen diffusion – so be ruthless when it comes to clearing out invasive plants.
As the water temperature rises, fish – being cold-blooded creatures – become more active and need to eat more as a result. This leads to larger amounts of waste being produced – fish turn around a twentieth of the food they consume into ammonia – which inevitably places greater strain on the filtration system. In addition, since fish need to fuel their current activities while also gaining enough reserves over the summer to see them through the coming winter, the sensible fish-keeper will provide high protein food once the pond water reaches 14 degrees C.
The higher the protein level, the more ammonia produced – potentially putting what is a prudent summer feeding regime on course to drive elevated ammonia and nitrate levels in the pond. While it is obviously essential to install a bio-filter which has sufficient capacity – and some to spare – to deal with the volume and stocking levels of your pond, the only way to be certain that your system actually is doing all that is demanded of it is, once again, to test the water to make sure. While ammonia and nitrite levels around zero are, of course, comforting, high nitrate readings bring their own potential problems.
Green Water and Blanket Weed
As the days get sunnier and nitrate levels rise in the pond, there is the ever present danger that algae – either the “green water” variety or the long strands of blanket weed – will appear. Nourished by excess nutrients coming from left-over fish food, fish faeces and rotting plant material, algae can be a major problem – especially if they are allowed to become established. Fortunately, with the development of ultra violet clarifiers and a whole range of chemical, organic and technological control measures, neither green water nor blanket weed should pose a permanent problem – especially if the elevated nitrate levels are spotted early enough.
The ideal summer pond should involve little more than checking the water level for evaporation and topping up as necessary or thinning out floating and marginal plants, as and when required. After all, it is summer time and the living is easy – or so the song goes – and with vigilance and a little judicious maintenance, it should be possible to make sure that it stays that way.