The tank looks nice and the controls for the camera are fine. What you could improve are the controls for placing plants and stones: Instead of the x,y,z arrows it would be nice if I could move plant with the mouse along the ground surface (adjust the height automatically). For the other props (wood & stone) it could be nice if they could just be dropped and are then placed via a physics simulation using colliders.

I had a bug once where one of the fish was trapped outside of the tank.

Neat! I think it's a solid base for an aquarium sim. I know you weren't asking about the art as much but I actually really liked the leopard cory. I wasn't sure entirely what I should be doing if water quality went down or anything like that, but it was fun arranging things and adding fish. Ideally I think you would want money to start at a positive value so that players don't start in the negative, although I suppose if there is no penalty to having a negative balance then starting off that way does tell the player directly that they can spend as much as they want. The only real bug I encountered is that if you changed purchase menus, it would still be registering my clicks on the previous purchase menu unless I closed the previous menu manually. Not a major issue but it took me a second to release that I was placing rocks instead of fish.