i recently purchased a 20 gallon fish tank and the shop keeper gave me a liquid its name is yellow liquid as written on the bottle he told me that it will prevent fish from getting sick and on the label of the liquid container it is written that it prevents lics fungual infection and other ailments and put 5 drops per gallon of water so i put a few drops it made water in the tank little yellow in colour but the fishes are seems to be alright so should i put this liquid every or it is harmful for fish and one of my friend says that do not put anything in the tank other than water condtioners please help