I dont think even white pvc lets too much light through not 100% on that. Most of your light is probably coming from the entrance and the outside of the tank. If you wanted to mitigate this, you could make a small cover for the outside of the glass that wouldnt let too much light in, and you could easily remove to view. Then maybe glue some fake plants to the entrance, or use some larger rocks to cover most of it, making the cave a bit longer. Just bouncing some ideas off ya, great idea!

