Heater question

[muck]

I don't believe that a 50W heater would heat a 50Gal tank.
I have a 100W Ebo in a 50Gal right now and it won't raise the temp over 75°F.
Think I will have to switch it for my 200W in my 15Gal tank...

Anyways maybe a 50W heater is underpowered for your 20Gal tank.
I would take Arty's advice and test with a different themometer.
If the readings the same you may want to get a higher wattage heater.