Micro leak in water cooling loop?

I recently built my first water cooling loop(so much fun, and sore fingers). 2 weeks into it i noticed that I was very slowly losing water. I figured "eh its probably still bleeding." So I topped it off. 2 weeks later, its still losing water. I've gauged it and it seems to be about 1-2 ml a day if I run it 24/7. When I had built it I had an issue with one of the fittings sealing so I figured maybe it needed some Teflon tape, so today I drained it and re-did the fitting. Then I let it bleed and topped it off for a couple hours before work. I just got home from work and after 6 hours of running it had lost about 3ml.

Tl;dr: how can I determine where this water is leaking from? There are no visible drops or fittings that are loose. I think UV dye would be my best bet, but I've heard that dyes sometimes gunk things up.

Get some strips of newspaper and wrap every fitting. If that doesnt show results, make sure the fill cap for the reservoir is sealing right, you can lose a fair bit of water to evaporation without ever seeing a leak.

Teflon taped fill cap, seems to have slowed the leak. Guess I'm looking for a better o ring on that cap. Thanks for the help

Keep us updated and glad it worked out.

After Teflon tape, a new o-ring, and a bit of silicone grease, it ran 6 hours without losing anything! I also put tissue instead of newspaper and no fittings leaked so it looks like its all good. Thanks guys.

I would replace the fitting that didn't seem right. I had a angle fitting on me after almost 3 years of use, finally started to leak after 4-6 re-installs. You're most likely fine but I personally like to take the extra precautions. I see it as a few bucks vs. thousands.