Help with false-bottom tank!

I am currently using a false bottom setup. At first, the humidity was high (86%) and the temperature was adequet (87.5). But over time, when everything starts to cool off, the temperature stays the same but the humidity drops to about 50%. I mist a few times, and it goes up to about 68% but then it drops right down to in the 40's. I have an aquarium glass top over top of the mesh screen to keep in the moisture, but it seems that when the substrate cools down, I lose all the humidity. Do you have any ideas/tips you could give me? They show you how to build it, but not how to maintain it. Thank you for taking your time to read this.

Where are you measuring humidity? Most humidity gauges SUCK and only approach accuracy when they're right on the substrate.

If the substrate looks dark, chances are it's humid enough. If you're worried just add some more water to the reservoir.

I'm measuring the humidity at the top of the tank. There is condensation on the walls at all times. When add water in, are you supposed to put it in the tube to the water at the bottom or just over the substrate? Last time I added it to the water at the bottom, it got pretty much flooded because it wasn't evaporating. Do you have to keep the water on the bottom warm? Or does it not matter?

As long as there's condensation on the walls, you're fine. Don't worry.

thank you all for your help!

Measuring from the top of the tank will measure more the humidity outside the tank than in.

And yeah, condensation on the walls = plenty humid. Most people pour the water down the tube (not a LOT, just enough to fill in where the gravel is). I pour directly on the substrate for my tanks that don't have false bottoms.