Hello.
I am a fan of arduino projects, but I'm only beginner, but I have an idea.
Aquarium temperature indicator (ds18b20) with 16x2 LCD (showing actually temperature) with B10K potentiometer, and automatized fan (5v ventilator). The best water temperature is for my shrimps is 23-23.5 C degree. In this case, the fan must turns on under 23.5 C degree, and turn off in 23-23.5 degree.
I have Arduino mega2560, Uno, and nano. But, when I must, I buy Mini.
Can someone help me??? Writing a programe, and make a shematic picture of this project.
Hi there,
I was browsing what other kind of problems people are having and seen your post.
Based on what you wrote it doesn't seem to be a very complicated thing that you are after. Sounds like a school / uni project tho. If you are still looking for a solution to this (it has been 18 days after all) I would suggest you have a look into relays (this will switch your heater on and off) and a waterproof sensor (ds18b20 does the job and is cheap).
In a nutshell what you want to do is to monitor the water temp with the ds18b20 (every 2 min) and when it drops under 23 you have to activate the relay that switches on the heating of your shrimp tank. This will obviously need to be battle tested to get the times between measurements and for how long to keep the heater on to get that goldilock settings 
I never played with the LCD screens but I am sure there are tons of youtube videos + tutorials how to do it.
And any of the Arduinos you have at the moment will do - no need to buy another one.
Hope this helps