I can share this: I had direct sunlight on my tank and did not know this for about a month.
One morning I was sitting at the breakfast table and noticited the issue.
I had a large outbreak of green hair algae on 50% of my rocks and had no clue.
Well, 4 months later & 100 additional hermits the problem is starting to go away. The natural sunlight can be a big headache, well for me it was.
Keeping the sun out: The quick fix, :thinking: I went to HD and bought one of those paper shades and cut it to the size of the doors glass and no more sunlight.
The perm fix: We are having 0 light cellular shades made to cover the french door.
Good luck.