වතුරේ තියෙන නයිට්රේට් ,ඇමෝනියා ප්රමාණය මැන ගන්නේ කොහොමද ?
There are test kits.... Check aquarium stuff suppliers.
These kits can measure between 0 -160 ppm or thereabouts. You have not mentioned why you need this for.
For other purposes you need an instrument with an ion specific electrodes (ISE). The can do 0 – 1,000 mg/L and is accurate to +/- 10% but are expensive.
Also there are other chemical methods but cannot be used at home.
There are several methods including spectrophotometric ones too.