Evaperation!!!

[Reef Pilot]

I have acrylic lids on my upstairs tank, and lexan on my downstairs tank. I clean them, maybe every couple months or so. And no salt creep. No fish jumping out, or humidity in the house. Doesn't seem to affect lighting either, and corals growing great. I will say lexan is better though, as it does not warp or lose its shape, and you can get by with much thinner material.