Home made UV dyes

[Diverge]

I need some suggestions for the amount of clear UV blue drops I should put in my loop. I just redid the whole water loop, and used a little less then a 1/2 gallon of distilled water. First I put like 4 drops, and hardly see any color in my T3 res w/ the lights out. then I put like 4 more (8 total) and I still don't see much.

I put like 4 drops in a 1/2 filled 0.5L bottle of water (so I guess like 0.15L of water) as a test, and can see it. It's not crazy bright or anything.

Are my expectations too high, or am I just not putting enough in?