What is a "tight fitting lid"?

[mythesis]

This lid has a 1cm grid. I had to make a small cutout in the back for the light mounts, but it rests right against the mount.

For some of the fish I'm looking it, it's recommended a 'tight fitting lid', does this qualify or does the grid need to be smaller?

 

[rhitee93]

I would say that qualifies in general. Fish smaller than the 1cm openings in the screen might still jump through the mesh, so you have to keep that in mind.

 

[Dread Pirate Dave]

That's pretty tight but I was wondering the same the other day and came across netting on BRS that is 1/8 inch.
https://www.bulkreefsupply.com/1-8-clear-netting.html

 

[Timfish]

If a fish is smaller in diameter than 1 cm it can get through the mesh. It might be unlikely but it's surprisiong how small a hole some fish can get through.