I;m going to say "Humidity lays low"

[LarryMac]

I took the top off complete while doing maintenance and during that time the humidity dropped 1%.
Valid responses:
1) Yes, that's correct and has been my experience
2) Never thought of that
3) Duh
...

[Ray]

Would we be correct to assume that the thing you took the top off of was a terrarium?

That seems entirely plausible for one or more of the following reasons:

• The top wasn’t very “tight” to start with.
• There level of air movement within the room may not be sufficient to significantly disturb the “bowl”
• Your RH meter is not “instantly” responsive.

[rbarata]

A drop in humidity is expectable but one of 1% is almost nothing...unless my interpretation of your post was not correct.

[DirtyCoconuts]

humidity (and air temperature) do "fall" with gravity if there is nothing to disturb them like a breeze or falling onto something.

if, as Ray suggested, the air is still in the place where the tank is, then it would mostly hold in the humid air

[Steve83]

Is this in reference to a take the top off, a terrarium/vivarium? You really only get decent airflow if there are vents along the bottom and venting at the top. They used to be referred to as Euro vents.

[LarryMac]

Originally Posted by Steve83

Is this in reference to a take the top off, a terrarium/vivarium? You really only get decent airflow if there are vents along the bottom and venting at the top. They used to be referred to as Euro vents.

Sorry, it's a paludarium with a waterfall.
The top fits snug.
There is 1 vent near the bottom.
There is a small fan set on low.

[SouthPark]

Originally Posted by LarryMac

I took the top off complete while doing maintenance and during that time the humidity dropped 1%.
Valid responses:
1) Yes, that's correct and has been my experience
2) Never thought of that
3) Duh
...

Dropped 'by' 1% of the usual value? Eg. if it was usually 80% and then it went to 79%?

[rbarata]

Originally Posted by SouthPark

Dropped 'by' 1% of the usual value? Eg. if it was usually 80% and then it went to 79%?

That was my interpretation too.