keep the water at the same level? you mean like.. topped up? or keep the water heated at the same level?
i like to put my heaters near my filters so the water is flowing around them all the time.
the heater will only turn on when the temp drops below what it is set to. you can see that it's on when the little orange light is shining.
to turn it lower you just... turn the knob lower lol. to turn it off just unplug it.
when you set up a heater, theyre not always accurate so you should set it and watch the tank for a few hours and then adjust it however many times you need to to get your correct temp. once you find the correct temp, just leave the heater alone. when the tank needs to heat up a little bit, the heater will go on by itsself. (orangish light)
make sure you get the heater with the right amount of watts for a 20L. im not sure how many gallons that is.. but when you get your heater it should say "___ watts. for ___ gallons/liters"
i hope i read this question right.
