I cleaned the sides, removed all the decorations, and started cleaning the rocks with the gravel vacuum. I was half way done when I saw a tiny blob that I thought was a bit of rooty material from one of the plants. When I moved the vacuum to suck it up, it darted away.
Awestruck, I quickly realized that it was actually a very tiny fish. It was less than a centimetre long, orange with black fins. I think it might be a Platy. Strange thing is, I only have 1 Platy in my tank.
Of course now I can’t find the mini fish. When I could see it, I noticed it was hugging the bottom, and hiding in amongst the rock. I worry that I somehow killed it during the cleaning, but maybe it is just camouflaged really well right now.