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Water Quality

Here are some handy tips to ensure that your pond always has good quality water in it; for the benefit of your fish and the aesthetics.

23 October 2020
Water Quality

Pond water test kitThe 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.

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.

Below, you will find a table complete with a list of chemicals and the suitable ranges of each chemical along with any suitable treatments that can balance these chemicals in your pond. Below the table will be extra information regarding each chemical.

If you have any queries, please do not hesitate to contact us for more information.

Chemical Ideal Range Treatment Description




PondXpert’s Tap Tonic

Blagdon’s Fresh Start

Tap water contains Chlorine and Chloramine which can be fatal for fish.

The Chlorine/Chloramine will naturally resolve itself if you leave your pond for 6-8 weeks or if you use rainwater. 




Ammonia: 0-0.25

Nitrite: 0-0.25

Nitrate: 0-5

Blagdon Ammonia Remover

PondXpert Gel Balls

Ammonia is created from decomposing organic matter and sludge at the bottom of your pond. Ammonia is converted into Nitrite and then into Nitrate. This is the Nitrogen Cycle. Your bacteria should control these chemicals, but treatments may be required.

AVOID over-feeding fish, adding fish to a pond with poor water quality, water changes and sludge at the bottom of your pond.



Add Baking soda (1 cup of baking soda per 1,000 gallons)

Calcium Carbonate

The Carbonate Hardness levels (or Alkalinity or German Hardness) need to be high in your pond water; this helps the nitrogen cycle to convert the Ammonia and Nitrite to Nitrate. Without the Calcium Carbonate there would be no biological filtration which would be bad for your fish.

Carbondate problems are uncommon. But adding rocks around the sides of your pond or waterfall can help.


pH: 7

Blagdon pH Adjuster (Acid)

Blagdon pH Adjuster (Alkaline)

pH has a 0-14 scale indicating the acid and alkaline levels in the water. 0-6 indicates too much acid, 8-14 indicates too much alkaline. 7 is considered neutral. The Digital PH Tester can identify your ponds pH level.

Your fish will be stressed with a pH between 4-6.5 or 9-11. Your fish may not grow, reproduce or they may die with a pH between 5-6.5. Your fish will almost certainly die with a pH less than 4 or greater than 11.


Oxygen levels between 7-9mg/L.

See our two blog posts:

How to improve aeration

Benefits of aeration

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.

Fish gasping at the surface or near waterfalls/fountains indicates low oxygen levels. If left, fish may die so in addition to your pump and filtration system, adding an air pump is vital.     


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