Yes. All the natural waters have some ammonia dissolved in it. Mostly, ground water tends to be contaminated with fertilizers which increase the dissolved ammonia in water.
No, one should not indulge in such practice. As changing the testing procedure can alter the results.
It depends on the pH of the input water. Acidic pH of the input water is makes it possible for the RO to remove 80-90% of the ammonium. Increasing pH of the input water decreases the efficiency of the RO as ammonia remover.
Expiry date of the kit has been specified on the kits. However, kits should be used within one year of the opening of the reagent bottles.
Between 1.0 to 1.6 PPT
There are several methods like using Zeolite, Yucca Extract, Partial Change of water, using probiotics etc. Cleaning is the key. Keep your tank/pond clean and you will not get any ammonia spikes.
Using Acids and Alkali shall change the pH. Some common chemicals are:- Acids ( Citric Acid, Tartaric Acid) Alkali ( Baking Soda, Calcium Carbonate)