This two page spread in my Stillman and Birn Alpha Hardbound sketchbook was prepared in advance using Fluid and Iridescent Fluid Acrylics. It was exactly what I was looking for to capture some small sketches of different tanks as I passed by. There was quite a bit of acrylic on the surface here. I didn't think watercolor would take well enough to it, nor provide enough variation in terms of light colors, so I used a tiny gouache set that I made out of a mini Altoids tin and Sculpey clay.
I came upon a huge tank of jellyfish lit from above in a very dark room. I was almost hypnotized by their beautiful floating, changing shapes and subtle coloring as they glowed in the light. I used white gouache against a dark golden-colored background, but felt it wasn't quite dark enough. When I got home, I darkened around the painted shapes with more gouache, letting some of the iridescent gold peek through.
The coral was behind glass, and I sketched it with a Kaweco Extra Fine nib fountain pen, filled with Noodler's Midnight Blue. I didn't think it would take to this surface, but it surprised me and did just fine! I used a waterbrush a little to spread some of the color for shadow areas.
Next up were some of the brilliantly-colored fish from the coral reefs. They were truly in perpetual motion, but I did the best I could. The blue fish in the top right box was such a bright color that I don't think he could be duplicated in paint, but I tried!