So, I don't know what your schedule's like, but if you're in Kyoto on the 21st, the Toji flea market is incredible for souvenirs, antiques, and kimono (f you're into that stuff)! I'm so jealous--I wasn't into aquascaping when I did my study abroad, because I totally could have squeezed out a trip to the ADA gallery. Ahh. C'est la vie.
I can't speak for aquarium equipment, but if you like just shopping, Nambaa/Shinsaibashi in Osaka is incredible. I spent so many weekends there just walking up and down the arcade
Edit: Forgot to menton--You can't hit Kyoto without going to see Kyomizudera. Big, orange temple, can't miss it.