Question..

[ainsleythurston]

I have a five gallon aquarium and my male betta lives in it.. First off, I only put like 2.5 to 3gallons of water in it.. I do not have a filter and I change his water every 4 days.. Is a 4 day water change too soon, do I need to wait more like a week? My second question is I cannot get his temperature steady.. I have a light in top of his hood and I leave it on and I have a heater.. I leave the light on pretty much during the day and it stays around 80 to 82 degrees.. At night I turn the light off and it drops back down to about 75.. I have a mini heater in the aquarium that is set for 75.. I want to keep it steady around 80 because where I have read they thrive the most around 80 degrees.. He use make a bubble nest or blow bubbles around the tank.. after i injured him accidentally, he hasn't blown ne bubbles.. Is it maybe because the temperature keeps fluctuating or what?

 

[fisch]

The temperature fluctuation can stress the fish and change his behavior. It could also be diet. It should be a little more varied than just the betta food.
You might as well fill the tank up. It will help with the temperature swings. Do you have a top? Just to make sure he will not jump.
Is your tank cycled? Do you know your water parameter measurements (ammonia, nitrite, nitrate, pH)? If you have ammonia and nitrite readings you should change your water more often. If you get zero for both of those you can keep the same schedule or decrease slightly.
You may want to pick up a small filter. Maybe one of those nano hang on back filters. It will create some flow without bothering the betta too much.
If you don't have live plants you can back off how long the lights are on. That will help keep the temperature cool too. I'd invest in a timer if you don't already have one.

 

[HN1]

No, that is not too frequent. In fact, more often may very well be better since you have no filter.

Set your thermometer for 80 and it should be ok.