All at the same time ie. multitask (something arduino cant do)
You mean "something I wasn't able to make the Arduino do".
Try looking at what others are doing with Arduinos.
This aquarium controller is doing just as much as your project - Arduino Powered Aquarium Controller Project | Marine Aquariums South Africa
GardenBot is an excellent modular system - GardenBot - open source garden automation project
HydroBot does all yours does, and serves a pretty smart looking web interface to monitor and control it - http://www.cs.helsinki.fi/u/ljlukkar/hydrobot/