Codling Badly: Yes I expect the Arduino to control the pump, but the pump will be circulating the fluid at constant speed; so I'll only need the Arduino to shut it off when the temperature reaches a certain degree.
I'll be recording the temperature with mini-log temperature recorders placed in the Storage tank, Jacuzzi and nearby outside. I'll be using excel to display my results (if that's what you mean by post-processing)
I don't understand what your asking with "Tracking time"
Yes I'll be working with an actual jacuzzi, the owner is my dad :/. And the pump will be circulating the fluid between the Solar panel and the Storage tank. The jacuzzi is separate and is currently heated by electricity (I'll only be measuring the heat loss and it can easily be reheated for the next day ) .The pump and the storage tank are items my dad bought from the company he was working for (which was closing) 20 years ago for a good price; he hoped they would be useful someday, well, today's the day!
Modeller: yes I know temperature and amount of sunlight are variables, I'm collecting data for the temp outside and at the end I'll contact enviroment Canada for the specific amount of sunlight those months to add in my essay.
terryking228: I'll be using minilogs to record the temperature, I can put the data on my pc to organize it in excel. Thanks for the links, if I have any future questions/concerns, I'll be sure to contact you.
arduinohabib: thanks, I guess I'll go with the UNO.