To drill or not to drill

GE silicon 1 is safe. Stay away from #2.
As long as you have a good bead of silicon on the acrylic you will be fine, you can even use gel glue to make the initial bond.

I would be more concerned about fish going over a straight cut than I would the slots.

 

OK, so the #2 is bad, don't believe everything you read on the Internet I guess... When I was comparing the two the only discernible difference was the cure time. No big, I will take it back and get the #1.

I will maybe cut some saw kerf width slots in the overflow and only cut them shallow and see how that works out. I plan on testing the thing in the next week or two and I guess I will see then.

My wife will kill me because she was so pissed off every time the little yellow watchman ended up in our wier. It made it to the sump once and it took me two weeks to catch him. I ditched that and did the PVC overflow in the current tank with a bunch of thin slots. I have not had that problem since. But she still said, "No slots" so I maybe in for it...