NT Labs
Diagnosis Tool Dosage Calculator Stockist Finder

Pondlab - Hardness Test


What is KH?

KH, also known as Total Alkalinity or Carbonate Hardness is a measure of the buffering capacity of the water in your pond. The buffering capacity refers to how well the pond can resist changes in pH.

Why test for KH?

Established ponds tend to acidify over time. This decrease in pH is due to the release of organic acids by the fish and the release of acidic substances by the beneficial bacteria in the pond and filters. The buffer in the pond counteracts this change by effectively ‘mopping up’ these acids preventing the natural drop in pH. If the pond was allowed to drop in pH the fish would become very sick. Ponds with excessive algae can show large pH fluctuations on a daily basis. This change is prevented if there is a sufficient KH. It is important to regularly check and maintain the KH as it will eventually run out.  

What do I do if the KH level is wrong?

Check the KH level of your tap water (or spring water etc). If the level is above 6°dH then regular water changes should keep the KH value in the pond topped up at a reasonable level. If the KH value is below 6°dH then perform water changes and boost the KH of the pond using Koi Care KH (Buffer) up. 

To maintain a healthy KH level in your pond use regular additions of Koi Care Mediclay. If you have a low KH level it is vital to regularly check the pH of your pond, to ensure it has not dropped too low.

What is GH?

General Hardness is a measure of the sum total of minerals dissolved in the water. Water can be either ‘soft’ or ‘hard’ depending on the amount of dissolved minerals, (the more minerals the greater the hardness).

Why test for GH?

The dissolved minerals that make up the hardness of the water are all essential for the biological processes that occur in the pond. If the hardness is too low then these process cannot function sufficiently, and the pond will begin to stagnate. Regular testing is essential, as the GH will decrease as these minerals are used up by the pond life. 

What do I do if the GH level is wrong?

Test the GH of your tap water (or spring water etc). If it is above 8°dH then regular water changes should ensure the GH is topped up.  If your tap water is below 8°dH then use Koi Care GH Minerals Up. This can also be used to boost GH in healthy ponds. If the GH value is low then it is vital to check the pH and KH of the water as well.

Try the Pondlab 200 Multi-test!



Available in the following variations:

Contains 80 Tests

Stockist Finder

Simplified map of the United Kingdom.

Find your nearest NT Labs Authorised Retailer in the UK.