20g High setup - first saltwater tank

[gregzz4]

Heya
When I suggested to raise the heater to the waterline on the heater, I was referring to the manufacturers water mark on the plastic body below the control knob. If there's no water mark, just raise it up so the waterline in your tank is about halfway between the top and bottom of the plastic on the heater control body.
Essentially you want to get the so-called 'sealed' plastic portion of the heater out of the water as much as possible, but without exposing the glass to a dry environment.
This will also make it easier to adjust as you're not putting your fingers in the tank.
Hopefully the suction cups allow you to do this and have the control knob clear the trim on your tank.