2 yr old Betta Fish, too late to add heater?

[khyber]

My boyfriend moved in about 6 months ago and brought his beautiful male Betta fish he's had for nearly 2 years. We got him a bigger tank - a giant cylinder vase that's about 6 gallons I believe. We then also got a female Betta who's fairly tiny, and put her in a separate, slightly smaller (4 or 5 gallon) giant vase / tank right next to his. They sometimes blow bubbles. Both have rounded stones covering the bottom of the vases, with bamboo stalks/plants, and some fresh aquatic plants (although hers got really black/mildewy within a month so we changed them out). We change the water weekly, clean the tank of any brown/black-ish mildew, and add water conditioner to the tap water.

The thing is: we don't have heaters. They sit next to a window that has a bamboo shade on it, so they are out of direct sunlight. My boyfriend had his fish in New York, but they are now here in Southern California. We leave near the beach so the weather is moderately warm year round. The female is super fiesty, swims all over the place. The older male has seemed more lethargic as of late. I was worried about the cooler temperature of their water since we don't use heaters as I've read is important, but would it hurt them to add a heater now since he's never had one? And what about an aquarock / oxygen? Again, my boyfriend has had the male Betta for nearly 2 years and its been doing great, has always been perky & happy, so would it even matter to add a heater now?

The only thing is this last few weeks the male Betta seems to like to wedge his body between the bamboo poles in this little u-shaped piece near the top of the tank and just sit there, not moving, for hours. I don't know if he's sleeping, resting, or something is up...?

Any advice would be helpful - thanks!

[TequilatheBetta]

it's never too late to add a heater :) I'm sure he'll enjoy the extra heat!
and about the wedging, bettas like to rest near the surface. You could try adding a plant with large leaves, so he could rest on the leaves.
can you take a picture of their homes? i've never heard of such a large vase before O.o

[Littlebittyfish]

Welcome to the forum.
Do you have a thermometer? First, I would get a thermometer and keep an eye on the temperature throughout the day,it will help determine if you need a heater or not. Bettas prefer warmer waters around 76-80 degrees. If you choose to get a heater.. it should be fine as long as you slowly raise the temperature. No sudden changes.