Not sure if its true or not but I have heard silcone doen't bond well to the plexiglass so baffles in your sump should be glass is your sump is glass
I am actually in the middle of making one right now for my 40 breeder -- I am using acrylic (( 1/4 inch, 1/8 inch bows too much )) baffles, and using silicone to hold them in place. This is the 4th sump I have built, and the rest were made the same way -- the oldest being about 8 years old now, and the baffles are still in place.
Whatever you use, make sure to get the bottom corners cut/rounded off -- most (( if not all )) standard tanks will have a silicone bead along the bottom edges; if you leave the corners normal it, most likely, not fit snugly at the bottom.
Need to upload better pictures, but this is from my old one -- to see what I am talking about;
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i am actually in the middle of making one right now for my 40 breeder -- i am using acrylic
not sure if its true or not but i have heard silcone doen't bond well to the plexiglass so baffles in your sump should be glass is your sump is glass