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The connections are not clear, how are you connecting the peltier element ?
Look at this for more power saving better than delayhttp://www.rocketscream.com/blog/2011/07/04/lightweight-low-power-arduino-library/
It is possible of course but you would need to use more than one pump (pump for each sensor) or use electrically controlled valves to open and close the water tube to each pot independently
Hi, There is another good modification that you should add. Imagine the case where the reservoir goes empty, your system would still run the pump and it would run indefinitely and eventually burn out (no water in the reservoir and the soil is dry so it will stay dry). A water sensor in the reservoir would be the idea and checking through the code.