What are the signs of good water quality?

amy35 asked:


Hi, I just want to know what are the signs of good water quality for fish, well in my tank I always do 20% water changes weekly. So I want to know what are the good signs that the water quality is good. (Please dont mention the test readings of ammonia and nitrate whether it is bad or good I just want to know common good signs).

PS: At least give 3 causes minimum and 10 maximum please.