More Betta Questions

It's been getting colder at the office... like low 70's over the weekend. I went out and replaced the strip thermometer with an actual thermometer and added a heater to my betta tank. I didn't like the idea of the dinky non adjustable, so I shoved a 5-15 gallon rated whisper heater in the tank. I've got my little guy at a steady 78 now. I'd like to have it slightly warmer, but I dont want him fried, so I've been taking the adjustments slowly.

My hex tank has an undergravel thing, that I removed the tube part from in order to make more room for the heater. To my surprise houdini pulled a disappearing act yesterday into the undergravel thing. Should I remove the rest of the undergravel filter when I change the water, or is it safe for my curious betta to play hide and seek with.

Also, today is my last day at work for 4 days. Should I give him some other source of food for the 4 days or should I just let him get hungry for thanksgiving?

His color is much better with the warmer water and he seems more curious of me. I hope he's not mad I took his lazy boy out of the tank. He used to sit up on the top of the air tube so he wouldn't have to swim to the top for air. Lazy fish huh?

Even though the strip thermo had up to the 76 showing color, the water was about 70-72 in the morning. Poor little guy was getting cold. Now I just have to get him a 5 gallon and maybe a little playmate.