Salinity is a build up of unwanted salts in the system and is a particular problem in areas of hard water.

It occurs because tap water contains salts which are not needed by the plant and which cannot be filtered out. This means that they remain in the system and build up in the nutrient solution.

An indication of salinity in the solution is the presence of scale similar to that found on the inside of the kettle.

This is why it is best to dispose of the old nutrient solution when replacing it with a fresh batch, to get rid those unwanted salts left by the plant. Flushing plain water through the system a few times and then removing it will also help.