The more you put in, the brighter it will glow, and also the more you put in the more you will notice it with the UV lights off. Too much can make the water cloudy and reduce the amount of glow. If you have a reservoir, start with 2 or 3 drops, if not start with 1 or two, let the water circulate so it gets mixed in, add a drop every 60-90 secconds until the desired amount of glow is achieved. remember, 2 drops may be enough!
Best of luck,
-Iron Hawk