Or make a pond netting top.
Egg crate is actually a light diffuser used in overhead fluorescent lighting in a suspended ceiling.
2 : not concentrated or localized <diffuse lighting>
For me the top for my tank was made from pond netting.
There is also a corner connector made from vinyl that I cannot find a picture of but look like these metal ones.
And of course the 3/8" pond netting.
I used 3/8 inch and double layered it. I had it single layered but my first yellow Head Jawfish jumped right through it. So now instead of one layer of a 3/8 inch square opening in the net i have the two layers crossed so that the square is a box with a X in it. You can see what I mean in the picture.
You can order 1/4" pond netting on line, however I did not only because I did not know if the fish would still be able to launch itself through the square hole. I was really surprised one day when my wife had my 2 year old granddaughter call me at work and tell me that the new jawfish was all dried up on the carpet!
all the supplies were from Lowe's except the pond net. They may even have that. Wish you were closer I would give you some. You could make a lot of covers from one package.
Don't have a full pic of mine but here is one another reefer made from the plans I gave him.
If you have a square tank it will be much easier because we had to trim for the bow front of the 29 biocube