Nice work here. Love to have one myself.
Was there any reason other than cost why Romex was used over bx cable?
Was a slanted roof an option as they tend to deal better with both rain run off and cooling.
Are you relying on ac to cool/dehumidify this room? Passive ventilation would have helped cut the electric bill a bit as well.
Consider adding a radiant barrier beneath the roof beams to help keep the room cooler. I'm in the process of a roof redo on my 1935 built home adding boh intake and ridge ventilation and a radiant barrier. The attic is unbearable so One of the goals is to passively cool that level to make it livable during the summer months.
Anyway, you have the best fish room I've ever seen here. Keen to see your filtration and plumbing progress ahead.
All the best,
"I am Groot", the faithful protector