Oxalic Acid & Screen Bottom Boards?

hello,

I run all SBB hives. Will I need to make a board to slide in to cover the screen inside? I have boards that slide into a slat under but most are not flush with the screen, having an inch or so below.

Please help.
Thanks!

I didn't find the right solution from the Internet.

References:
www.beesource.com/forums/archive/index.php/t-288891.html


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