I'm glad to hear you're getting a bigger tank.
You should look into getting a
test kit. The
API master kit is highly recommended. A little pricey but more accurate than the strips and less costly in the long run.
When ever fish start acting weird the first thing to do is rule out water problems. If you have excess ammonia or nitrites both are toxic to fish. The water could still be perfectly clear.
The only way to detect them are to test for them.
I could be off, I don't have live bearers. The members of the forum have a wide range of knowledge so hopefully others will be able to help you further.
Good luck.