Shrimp slowly dying

[NateB]

Had the tank for a couple years. Last maybe 6 months the macroalgea went from taking over to almost gone. Had at least 20 shrimp. Now only 4-5. Snails are doing fine and reproducing. Checked salinity; it’s good. Have a grow light on tank. There is a film at the bottom under the rocks that looks suspicious? Thoughts?

[Mustafa]

What and how often do you feed? Does the container have a lid?