Water quality tests in the lab
Monitoring nutrients and harmful algal blooms (HABS) in water

Water hardness

What is water hardness?

Water hardness measures the amount of dissolved minerals in the water (mostly calcium and magnesium). It is related to alkalinity, as both measure calcium carbonate content.

Why is water hardness important?

Water hardness impacts many other processes in aquatic environments, so it is one of the most common water quality tests conducted. Calcium, in particular, is a very important part of many of the biological processes in fish. Water hardness also affects how toxic various metals are to aquatic life. If the water is hard, dissolved heavy metals (zinc, copper, etc.) will be less toxic to aquatic life than if the water is soft.

What does a hardness measurement mean?

Ever washed your hands in hard water? Did you notice that with hard water you need to use more soap? So, you can imagine how having more dissolved minerals in the water may affect the fish living there. Find out what species live in your body of water and what their ideal hardness is. This way, you can track how hardness trends impact your fishy friends.

Some common values

The levels of hardness are classified as follows:

Soft0 – 20 ppm
Moderately soft21 – 60 ppm
Moderately hard61 – 120 ppm
Hard121 – 180 ppm
Very hard>180 ppm

Water Rangers testing protocol

For this test, we use Taylor Pool and Spa Test Strips. Learn why we selected this brand and our research on the accuracy of various strips.

Pro Tip: If the colour on the test strip appears in the middle of two colours on the bottle, you can record the absolute middle (for example, if the colour is somewhere between 100 and 200, then record a value of 150).

How to test hardness

  1. Rinse sample cup 3 times.
  2. IMPORTANT! Make sure your hands are dry, since moisture in the container will ruin strips.
  3. Shake out 1 test strip, close bottle.
  4. Dip the entire strip in the water. Remove after 2 seconds.
  5. Wait 20 seconds before reading.
  6. Compare colours with guide on side of bottle. Line up the colour strips vertically so that you can compare along the spectrum for each value.

Get hardness test strips here or as part of a testkit:

Contributing to the community!

Water Rangers is citizen-scientist led. So, if you have any questions, ideas, or notice any errors, please tell us!