I've got two fish with similar troubles, but we'll start with Ryou because he's the one that is scaring me the most.
Ryou is a pink veil-tail with blue and purple flecks in his fins and tail. I bought him in November after watching him sit unwanted at the local pet store for three months. He lived in a jar at my parents while I finished my visit home. After I came home I moved him into a simple glass bowl with glass stones in the bottom and a couple of glass candle cups for him to hide in. I change his water once a week, feed him twice a day, and talk to him when I cook (he was my kitchen fish). However, he's gone from cat-curious about everything, chatty, and dancy to laying around on the bottom of his bowl in a tunnel between his two hidey-holes in the last week. He still eats regularly and retains his excitment over it, but has stopped his other shenanigans almost entirely. I've moved him to my living room to hang out with my crowntail Arez to see if he was just lonely, but it hasn't helped at all. He looks healthy, although he does attempt to burrow under his rocks occasionally. He's scaring me, and I don't know how to help him.
The next case is Azazel. He's my little treasure-find, a dark dark body (blue or purple, its hard to tell), with red tipped fins and tails. And he's little, very very little. His early history is much like Ryou's, started in a jar for a week or so for moving purposes and whatnot, but he was much younger when I bought him in December. He's my flirt, he always used to fan up and wiggle around to get attention. He likes song, being talked to, etc. He was another very active fish. He did have a "jealousy" problem as I called it. He would hide from strangers and flare up at people he saw me give attention to (very strange, I know). However, he has stopped reacting to my voice now that I've moved him to the living room where I normally write with him. I shifted him into a larger bowl, because I've heard that they prefer the space, given him a little house - but similar trouble has occured. He keeps trying to get under his house. I've removed it now, and he has moments of acting his old self, but beyond that he just sits at the top of the bowl and does nothing, no matter how much I talk to him.
Have I done something wrong? I'm sorry, I'm not up to date with the pH chemistry whatnot. I've just been conditioning with AquaSafe in completely new water once a week, feeding them bio-gold twice a day, giving them blood worms once a week, chatting with them. I really don't know what else to do. I'm most worried about Ryou, and I don't know much about Beta behavior outside of that they are all unique.