Is that what that is sagging along the top of the tank? Is it symmetrical? I made one out of acrylic and it would slowly sag over time and I would just flip it over every month or two.
Ya its what is sagging in the middle. This one was my first attempt at a rimless top. The frame is 3d printed, so it lighter weight and more economical then an acrylic top. It is symmetrical from left to right, but not top to bottom, and its held in place by a couple tabs at the corners. Likely need to add those tabs in the middle as well to prevent the sagging, or revise the design so it sits on the top of the rim instead of inside it. I have gotten better at stretching the mesh on my newer ones so that the mesh doesn't sag into the water, but just something for me to consider on future designs.
Yep just got him on Saturday so I'm starting him low hoping he attaches to that rock which I can move up down the road. The lid does sag a bit now so the mesh is in the water and it grows some algae almost algaescrubber style but I just clean it off during my weekly water changes. Doesn't seem to be hurting anything.
He wont take long to attach, and unlike corals clams don't really need time to adjust to the lighting changes as they can self regulate.
If at sometime in the future you want to change out the lid, so it doesn't touch the water, let me know. I can try a different design, and Ill do it pretty cheap for you since, it would be to replace this one. Or I could even just print a few tabs for the middle that I could attach for you. You'd need to ring it to me for a day or so but would be pretty quick to modify the existing frame with those. That wouldn't fix the screen sagging, but it would at least keep the frame from sagging further