Jumpy betta

Question
I recently purchased a betta to one that had passed away due to an infection. Its been about 3 weeks now since I have had him, and initially he was very attentive, and ate well. In the past week, I've notice that he is no longer eating much, if at all, and is very 'jumpy' or seems nervous...meaning that he would dart around the tank very fast as if being scared. He won't let me look at him at all, retreating to the rear of hte tank to hide. His fins all seem to be fine, and I don't notice any change in his red/blue color or any symptoms on his body. One thing odd tho, as I have cleaned his tank twice so far. The first cleaning was almost after the initial 2 weeks. Left one morning with the water unusually clear (for being nearly 2 weeks), and when I returned home later that evening, the tank was all cloudy, necessitating a 100% water change. I did that again a week later. The water is kept warm, and he is still very 'active', not lethargic at all. Any ideas as to what may be the cause and cure?

Answer
Dear Eric,
That's a somewhat mystery one. There are several reasons why he may be "jumpy"
1.)My first thought was the water quality might be poor especially since the water is changed after 2 weeks which is really too long for a betta to go without a refreshment of clean pollution-free water. Depending upon the enviroment he is in-- vase, bowl, tank. Anything that is bowl or vase-like and is not filtered should be getting at least 2-3 times a week water changes insuring that the water is dechlorinated and equal in temperature to that of what he is used to.
2.) Perhaps he is not use to you quite yet. Some bettas take a while to get adjusted in their new home and enviroment and also they need to get use to their owners also. (I know this probably sounds ridiculous but it's true)
3.) Not enough security. Bettas without cover in the form of thick and bushy plants will often feel very unsecure and be prone to hide a lot. Live or plastic plants can be used but be sure that any plastic plants don't have sharp or rough edges that can snag and damage the bettas delicate fins. Arrange some plants on the surface as well.
4.) Personality. Some bettas are timid and some are very, very bold. Most bettas I have encountered and owned typically aren't as shy as you described yours being. I don't think it is just his personality and I would imagine other factors are contributing more so than anything.

So there you have it. Many things can influence a betta to behave in an odd why as you are seeing. Increase his water changes please if you can, give him some thick cover including fine plants floating at the top, give him some time to get use to you, even place a small handheld mirror to his bowl/tank so that maybe he will flare and this will greatly increase a betta's confidence especially since the mirror will be taken away later and he thinks "I won" yes, I know this sounds ridiculous too but that's just how these marvelous creatures work.

~Keep an eye on that little guy and I hope this helps!
Best wishes and Best of luck!
Karen~