Pond Water Quality Spikes – Nitrates

So although nitrates aren’t as toxic when compared to ammonia and nitrite, significant build up in nitrates can be equally detrimental to fish health. Nitrates in the UK, particularly in and around the London area, can be tricky to manage in ponds as the concentration in tap water can be up to 50mg/l. For most ponds, this means you’re instantly on the back foot as when performing routine water changes you’ll be adding to the nitrate concentration in the pond which is far from ideal.

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With nitrate being the last waste product produced by the biofilter, control of nitrates rests on management outside of the biofilter itself. To recap your knowledge of the nitrogen cycle and the biofilter, please read the ‘New Pond Syndrome’ advice page. When testing nitrates, values should be as close to 0mg/l as possible but in reality for a well stocked koi or goldfish pond aim for a value between 20-50mg/l. Values greater than 75mg/l and heading towards 100mg/l are dangerous and need to be addressed.

• 1. Increase the frequency of water routine changes

  Description text goes hereAs nitrates are the last product of the biofilter water changes are the most effective way to get rid of excess nitrates. Assess the routine maintenance of your pond and consider the frequency and quantity of water changes you perform. To control nitrate spikes you will need to increase one or the other, sometimes both!

  For ponds running on a ‘trickle in trickle out’ system, this alone is sometimes not enough to support the number of fish you have in the pond. In which case you will need to start performing routine water changes on top of the constant turn over of water from the trickle in trickle out system present.

• 2. Reduce feeding

  One of the most common causes for excess nitrates is overfeeding. Consider the amount you feed your fish. Food should be consumed with 2-3 minutes of feeding out. Any food hanging around for longer than 5 minutes indicates overfeeding, so reduce the amount offered at the next feed and repeat this process until all the food is consumed within 2-3minutes in one sitting. Click here for our guide on feeding.

• 3. Assess stocking density

  The more fish there are in a system the more waste they will produce. In some cases where water quality can’t be controlled using the steps given, it may be necessary to reduce the stocking density of the pond. Less fish will mean less waste and ultimately happier and healthier resident fish.

• 4. Bind nitrate at the source

  As mentioned, in certain areas of the country, tap water can contain >50mg/L of nitrates. Consider removing nitrates before they are added to your pond via the use of specialist binding agents, resins or filters. For a short term fix chemical detoxifiers such as ‘Pond Prime’ by SeaChem will bind and detoxify nitrate along with other toxins.

• 5. Add aquatic plants

  Plants utilise nitrates to grow so by increasing the number of plants in and around the pond will naturally decrease the levels of nitrates in the water. Consider protecting plants in baskets or in water features as koi in particular will quickly destroy vegetation!

• 6. Consider an Aquaponic filter

  Using the same logic as the step above, aquaponic filters utilise plants to reduce nitrates in a pond.

• 7. Use an alternative water source

  The use of de-ionised water or reverse osmosis (RO) water used in household aquariums to avoid high nitrates is not viable for ponds. Depending on location, some pond keepers are able to source water from alternative sources such as bore holes or spring water. For small ponds, consider whether rainwater is a viable option.

Consider increasing the number of plants in and around your pond to naturally decrease the levels of nitrates in the water.