Bottom of tank

Question
I have two betta fishes and ive had them for about a year. They live in one tank thats divided by a barrier. I noticed today that after i changed their water, theyve been laying at the bottom and breathing heavely. They also seem to be trying to stay there. Ive tried everything.

Answer
Dear Emilia,
Is this your bettas first water change? Have you done anything different to the replacement water?

Did you insure the replacement water was properly dechlorinated and equalized in temperature to their aquarium?

What is their temperature?
It sounds like they could be into shock from the water change if the replacement water has not been dechlorinated or equalized in temperature to what they are accostumed to.

Knowing these things will really help!
There's not much I can honestly say for you to do when the bettas behavior can be caused by so many things and not knowing if anything has been done different or if the replacement water was treated properly.

I really wish you the best and followups are welcome!
Karen~