from my understanding the chloride ion’s concentration is about 30x more than the nitrite ion concentration in the water, nitrite is toxic at sround 0.1 mg/l. so the chloride ion concentration would have to be at least 3.0 mg/l. so about 5.0 mg/L of salt, which is about 60% chloride, around 18.6 mg/gallon. A tspoon of table salt is about 5.5 grams. so a teaspoon of table salt would be enough for around 290 gallons. just add the salt, it won't hurt anything