BGK like subdued lighting, low light, they do not like bright light. The tank light coming on can cause him to be startled/shocked.
Perhaps turn on a light next to the tank to let the fish start to wake up with a low amount of light.
Add some plants layered over the top of the tube or maybe attach the I think you said you have plastic plants with a zip tie or fishing line (if you use fishing line, you can use multiple circles, tie off each circle and cut excess, in case it falls off, long curly strands can get caught on fish and I had some got tangled before when my round and round and round the rock tie job with moss fell off its rock) to make sure that you get to see him but the light coming from the top is maybe a quarter and kind of dark.