what % of screen top should be left open

Hi

I have a 40 G Tank and just covered the screen top with foil and tape. I already cut on window open for her to breath and lamp. Now I am about to cut out the second one.
Before I do, I would like to know how big I have to cut it. The one I cut was
6"x6". Wast you think what % of the screen does she need to be open to breath???

Thanks

If your not using heat lamp you can cover the entire lid. Screen tops arent air tight so with it fully covered youll get proper levels of RH.

:oops: what are RH levels?

RH= Relative Humidity

The RH level is excellent! Thanks
She survived the night as well I guess that mean she got enough air through the top. No I just have to get the temp out. unfortunately we have an other off school day and Pet go is closed today again.