Assertion: ammonia's ph | /r/HasProperty | tested as a rule of thumb
Facets:
value: once a month
type: TEMPORAL
Source sentences:
text: Fish and plant waste, water evaporation, topping off the water, and water hardness will all contribute to changes in the pH. As a rule of thumb, pH in an established tank should be tested once a month, and any time there is a fish death or illness.