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The Quality of Your Pond Water

The water in your pond is going through a series of biological transformations constantly. In fact you could almost think of it as living. Understandably maintaining a decent quality of water is therefore an ongoing task, not only is it beneficial to the appearance of your pond but essential to the health of your fish.

05 September 2017
The Quality of Your Pond Water

A DIY water quality test kit is a good starting point. The 6 in 1 test kit is straight forward to use if you are new to the process of water testing. It comes with twenty five test strips and you simply dip one strip at a time into your pond water and then wait for the colours to appear on the strip. Once the colours have developed fully, you compare the strip to the chart to diagnose your water. Other test kits are available to buy, but we would advise testing for Chlorine, pH, Carbonate, hardness, Nitrite and Nitrate. New ponds or ponds with problems should be tested two to three times a week, whereas established ponds with little history of problems can be tested monthly.


                                 Pond water test kit



Chlorine and Chloramine in Tap Water

Many new pond keepers do not realise that tap water and fish do not go together!

Tap water contains Chlorine, Chloramine and heavy metal which can be fatal for fish. To remove these from the water you can use a treatment such as PondXpert’s Tap Water Tonic or Blagdon’s Fresh Start. They will even add a protecting coat to your fish to guard their health and neutralise any traces of ammonia.

An alternative to using a treatment would be to leave your pond water for 6-8 weeks to let the Chlorine and Chloramine leave naturally before adding fish or you could fill your new pond with rainwater.


                              Fresh start water treatment to remove chlorine from Pond water



Nitrate and Nitrite

When a new pond is created the water takes time to mature and become healthy even if you used an initial tap water treatment. Firstly Ammonia peaks, followed by nitrite in the sixth to eigth week, then lastly Nitrate. This is called the Nitrogen cycle.

Ammonia is initially created from fish waste, uneaten food and fish respiration. In more established ponds high ammonia levels can also come from decomposing organic matter (leaves/ dead plants) and sludge in the bottom of your pond. Specific bacteria convert the Ammonia into Nitrite and then into Nitrate, at which point it is no longer a worry to the health of your fish and becomes a plant food (but this can contribute towards algae).  Over time the healthy bacteria in your filter should remove ammonia and nitrite but the pond balance is not always even so a treatment may be required at this point.

So in short try to:

• Avoid over feeding of fish

• Avoid water changes (unless necessary to remove other chemical imbalances)

• Avoid letting dead plants and leaves rot in your pond

• Avoid a build up of sludge at the bottom of your pond

• Adding fish to a new pond before good water quality is established


When testing your water remember that it is higher levels of Ammonia and Nitrite (ideal level being 0 ppm for both) that are harmful to fish and that high levels of nitrate can contribute to green water algae. It is worth noting that even low levels of Nitrite can cause stress to your fish.

Ideal Nitrites: 0

Acceptable Range Nitrites: 0 - 0.25

Ideal Nitrates: 0

Acceptable Range Nitrates: 0 - 5.0

Ideal Ammonia: 0

Acceptable Range Ammonia: 0 – 0.25


These products may help you with this:


                             Ammonia remover for pond water                    Nitrite and nitrate remover treatment for your pond






The Carbonate Hardness levels (often also referred to as Alkalinity or German Hardness) need to be high in your pond water as they help the nitrogen cycle to convert the ammonia and Nitrite to Nitrate. In fact without the calcium carbonate there would be no biological filtration which would be disastrous for your fish.

In general it is fairly uncommon to have problems with the Carbonates in your pond water, if your test results indicate a need to raise the carbonate hardness you can add Baking soda (1 cup of baking soda per 1,000 gallons), Calcium Carbonate, concrete blocks, oyster shells, limestone, or even egg shells to your pond. Adding rocks or concrete around the sides of your pond or to a waterfall can also help.

Readings from 50 to 200ppm (parts per million) are acceptable and it is suggested that 100ppm is a good level to aim for. Good carbonate levels will act as a buffer to keep the PH steady. 


                                          Oyster Shells






The pH of your pond water can be affected by multiple factors which are often out of your control. Concrete around the edge of your pond, rainwater, chemicals and fertilisers around the garden can all affect the reading.

pH has a zero to fourteen scale indicating the acid and alkaline levels in the water. Zero indicates too much acid, fourteen indicates too much alkaline and seven is considered neutral.


Your pH results

• pH 7.0: An ideal result for your pH test, as fish have an average blood pH of 7

• pH in between 4.0 to 6.5 or 9.0 to 11.0: Your fish will be stressed

• pH less than 6.5: Growth will be limited

• pH less than 5.0: Reproduction will stop and fish may die

• pH less than 4.0 or greater than 11.00: Death is almost certain


These products may help with this:

                                     pH digitial tester            Treatment for acidic pond water   pH adjuster for alkaline ponds





Oxygen levels

Lastly, the oxygen levels in your pond water are imperative for the health of your fish. In addition to your fish, things like warm temperatures, fish waste, algae blooms and decaying organic matter all decrease the oxygen levels. Even the good bacteria in your pond consume a lot of oxygen.

Look out for your fish congregating near an oxygen source or your fish gasping at the surface as an indication of low oxygen levels. If left, fish may die with the larger stock dying first as their oxygen requirements are greater. 

A dissolved oxygen level in the range of 7-9 mg/L is ideal for koi and goldfish to live and thrive.

So in addition to your pump and filtration system, adding Oxygen to your water with an air pump is a great idea especially in the summer months. 



                                       Air pump to add oxygen to your pond


As always if you would like to discuss any pond problems with a member of our team then please call 01642 370888 and good luck with your water testing!





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