I just got done setting up my fish's new tank and was wondering if I did everything correctly. In the diagram on my Elite Mini Submersible 25W heater's instructions it shows the knob on top above the water, but it says it's fully submersible. That means I can put it all the way below the water? It sounds like a stupid question because of the "fully submersible" label on the package and I've seen many pictures of heaters all the way below the water. It makes me a little nervous with the cord like that though.
Also, the instructions on the Aqueon 2.5 gallon tank says not to fill up the tank all the way for a while
"When all the interior work has been done, resume filling the aquarium most of the rest of the way... Do not fill all the way to the top. Leave about an inch of clear glass at the top. You will top it off after the fish have been added."
Can someone confirm if I am doing everything correctly and clarify the heater installation? What should I do next? How long should I wait to turn the heater on and put my betta in the tank? Thank you for any help! :)