Could you solve the problem you mentioned by shielding the overflow from light? For example, placing a piece of plexiglass or some other type of material above the overflow and painting it to prevent light penetration. This would prevent light from entering the overflow, but would also not hinder the flow of water.
I actually did try that and the heat of the halides warped the plexiglass I had. The dark color really absorbed the light. Once it warped light was able to start getting in.
Several ideas for intake strainers are shown on Rich Durso's website. I used a plastic mesh tube, the kind fish stores sell that go inside an overflow prefilter. The prefilter is replaced by the Durso tube anyway. Stick the mesh tube into the intake. Just use the mesh tube, don't use the prefilter media. You will need a 1.25-in to 1-in PVC adapter, assuming your Durso intake elbow is 1.25-in and the old prefilter tube is 1-in. The strainer on my intake extends all the way to the bottom of the overflow where I capped it with a PVC cap. So the filter is about 10-inches tall with plenty of surface area that takes a long time to clog, if ever. Easy to see and inspect. I have never cleaned mine (installed 4 months ago). Large algae fragments and snails can't get through the plastic mesh tube surface. The algae eventually breaks up and the very small pieces slip through the mesh and wash away. I got the idea from this forum. I'll post a link if I can find it. I remember there was a picture.
