I have been using
dye-lite from Caseetc for months.
It was originally designed to find leaks in automotive fluid systems. Place dye in radiator (for example) let it run for a bit, then turn on a UV light and look for leaks.
I have been using it for about 5 months with out any problems.
It lasts forever, about 5 drops does my whole water system. The effect only fades if you add water and dilute the solution. Also, when you change your water every 2 months (or so!) you will need to add dye to a new batch of distilled.
The dye does require blacklight in order to flouresce. I have 1 x 15" neon, and 2 x 6" neons. Only blacklights (or UV) cold cathodes or neons will work.
Lastly, if you have plastic hose barbs in your rig the white plastic takes up the dye (rather dramatically). This discolors your hose barb, and removes circulating dye material ( thus washing out the color). I have not noticed any similar problems with the pvc tubing.
Finally, a pic:
And "I am spent"
