EC / TDS / Temp meter

An essential part of any water growing kit is an EC/TDS/Temperature meter.

Electrical conductivity or EC is a very important measurement to take when working with nutrients and growing in water. An EC Meter measures the Electrical conductivity in a solution, good for measureing the amount of salts nutrients or impurities in water.

Total Dissolved Solids or TDS:

A measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular (colloidal sol) suspended form. TDS concentrations are often reported in parts per million (ppm).

https://en.wikipedia.org/wiki/Total_dissolved_solids

Temperature C & F is another important factor to take into account when growing in water. Plants will have trouble growing, if water is too cold or too hot. Getting a reliable reading of this is an important step before adding your plants to a hydroponics system, aquaponics system, or any other water growing system.