Yes, you should get your water tested, you may want to invest in a liquid test kit too.
When you clean tanks you should really only doing like 25% water change every week. Doing a full water change kills to much beneficial bacteria in your tank!
Hahaha ohhh no! Sounds like a heater I just got with my 20 gal I bought off a local ads site. The only thing you can do it play around with it. And slowly move it higher and keep a close eye on the temperature. It probably took me a full day to get it to the temp I wanted.
I don't really mind top fin I guess. I haven't owned to many products, I mean the filter does the job, it would just be nice if it was as quiet as advertised.