Thanks for all your replies friends!
Ok, I'll source a thermometer. It's comforting to know that you keep bettas in that size tank. The water changes are what I've come to know are very important.
Hi teeny, I'll get something to cover the bowl ASAP. The plant I have is this one (either this, or one that's very similar):
Nice cover Bettanewbie60 (I should have that name:/)
I got a wonderful half moon betta. I realized it was spitting out its food, because today is the day for 100% water change and tank cleaning.
What do you recommend for water treatment for bettas?