Nitrate in Rainwater or Tapwater: Topping Up Koi Ponds. Which is Better?
John McLauchlan looks at topping up your koi pond. He asks should you use tap water or rain water?
For almost 10 years, we have been selling microbial products under the brand name Viresco™ which remove nitrate in pond and aquarium water.
The main reason for using these products is to suppress blanketweed and other algae. Nitrate is the key nutrient ingredient because, when it is reduced to zero, algae, in whatever form, will die of starvation.
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However, a relatively small proportion of our customers use it because they know the condition of their fish is improved when the fish live in water with zero or very low nitrate content. As a result, we have regular feedback from these people to say that their fish are healthier, 'happier' and are 'different creatures'.
We also are informed that sores and flesh wounds heal up much faster when the nitrate level is taken down.
Tapwater
Most koi keepers who have ponds with bottom drains remove organic waste in two ways. They will drop their bottom drains, releasing the waste matter with a relatively small amount of water. They will also use vacuums to lift out the dead organic matter from the bottoms of their ponds.
In addition, many koi keepers regularly change relatively large amounts of water – up to 10% or more at one time.
When we ask the pondkeeper why he does this, we usually receive one of two answers. The first is to 'freshen up' the water and the second is to reduce the nitrate level.
Most people do not appear to check the nitrate content of the tapwater they add to the pond. When they do, they can find that the water taken out is, say, 60ppm nitrate and the water that is going back in from the tap is 40ppm! When we asked the Drinking Water Inspectorate what is the maximum allowable nitrate content of tap water is, they gave us a figure of 50mg/l (ppm) as their standard.
However, many of our customers have told us that the nitrate content of their tap water is considerably higher than this figure. Over the years, we have recommended that ponds be topped up using rainwater when the nitrate content of tapwater is relatively high. We have had, however, interesting feed back from some pondkeepers. Having used our Viresco™ product to keep their ponds clear of blanketweed, they have reported that blanketweed has grown back with a vengeance after a rainstorm.
Blanketweed after Rainstorms. Why should this happen?
We are certain it occurs, at least in part, because of something we have all heard about. The key to this phenomenon is acid rain. I would suggest that most of us have not fully appreciated the significance of acid rain in keeping ponds. Acid rain arises from two types of acid-forming materials. One is from sulphur dioxide that rises into the atmosphere primarily as a byproduct of industrial processes and from the burning of fossil fuels. From a pond keeping and algae growth perspective, these sulphur products are not important.
The second acidforming group of gases that rise into the atmosphere are the nitrogen oxides. These include nitric oxide (NO) and nitrogen dioxide (NO2). When these oxides (NOx) are dissolved in rainwater high in the atmosphere, mainly nitric acid (HNO3) is produced. This dilute acid falls to the ground when it rains and produces nitrate in ponds.
The sudden rush into growth of blanketweed after a rainstorm is therefore explained.
Another nitrogen compound that drops out of the sky when it rains is ammonia. It falls to the ground and into ponds as dilute ammonium hydroxide (NH4(OH)). It is an alkali, not an acid and the amounts are generally less significant for pondkeepers than is the nitrate arising from nitric acid. It is interesting to see that ammonia, one of the products pondkeepers are removing from pondwater through their filters, can appear in the pond water when it rains as well as from fish excrement.
The National Atmospheric Emissions Inventory
The website (www.naei.org.uk) of the National Atmospheric Emissions Inventory (NAEI) gives a good deal of information about the amounts and sources of various atmospheric pollutants by geographical region. Another set of data that is available from the NAEI website is a table that shows the annual tonnes of different pollutants emitted from various large point sources situated within different distances from a particular postcode. Much of the data has been produced from models used by the NAEI although some have been provided by the owners of the plants in question.
Pondkeepers can access this tool by going to www.naei.org.uk/mapping/mapping_2004.php and entering their postcode in the appropriate box. We suggest that pondkeepers go into the NAEI website and look further into the emissions that might be personally affecting them by using their specific postcodes.
Going back to the original question of whether tapwater or rainwater should be used for topping up ponds, the recommendation is the pondkeeper should check particularly for nitrate (and other nasties) in both types of water sources and, if possible, use the one with the lowest content. Pondkeepers also have to bear in mind that levels may fluctuate so regular checking is advisible. Better still, if pondkeepers practise water changes to simply lower the nitrate level in the pondwater, then they need not change large volumes of water because pond products, for example Viresco™, are available that will take the nitrate level down to zero and hold it there. Once nitrate is removed, blanketweed and other algae stop growing. However, there is no substitute for keeping on top of regular pond husbandry.
Contact Viresco directly to ask a question or to order using phone, fax or email