Hi,
I see that Aquarium water pump is made from DC motor, right?
I will use PWM to change it's speed. But I need complete documentation of system.
I need wiring diagram, and previous code that need to be modified, or even if you don't have all of that we can create one.
My background is Electronic Engineering, and my main job is Electronic designer & Firmware programmer. For arduino, I know both of its firmware and hardware. I have use it since 2013 for various kind of project I did.
Lets discuss the detail of this project over chat.
Let me help you for this project.
Best Regards,
Rijal