Hi there and welcome to the forum. In order to help you with your betta we need you to provide some information.
Can you tell us if you've done any recent changes in your tank? Added a plant or suppliment or chemical additive of some kind for example?
Is your betta losing color at all or slightly bloated? What shape are his fins in, rotten or the edges seem tattered/abnormal in color? Please let us know of any physical abnormalities you may see.
Is your tank heated? Betta are tropical fish and require water varying from 74 to 82 degrees to be comfortable. They become lethargic in cold water (and begin to shut down over prolonged periods of cold temperatures).
I recommend a partial water change of at least 30% if you've done one recently and if you haven't done one recently (in the past 3-4 days) then one large 50% water change of conditioned water that is nearly the same temperature as your tank water. If the temperature greatly varies when you add it to the tank the temperature shock will cause further stress on your betta. A stressed fish is a sick fish (and then a dead fish!). be sure to pour the water in slowly as not to disturb your betta and other fish as little as possible with the water movement.
Is your tank aerated or do you have enough water surface disturbance to oxygenate the water? If you have little surface agitation it makes it difficult for your fish to get oxygen, betta have labyrinth organs and while they can breathe regular air they still require well oxygenated water.
How large is your tank? 5gal 10gal, etc?
Please provide us with your water parameters from a new test, not numbers from yesterday or a week before.
Nitrates, Nitrites, Ammonia, Ph, alkalinity.
Is your tank cycled, as in you've let it establish a healthy bacteria colony so that your tank can house fish and keep stable water parameters? If you don't know what that is here is a quick link.
http://aquariuminfo.org/cycling.html
How often and at what capacity do you do water changes? You should be doing at least 30% Partial water changes twice a week or a 50% water change once a week. Please understand that these are water change schedules meant for an established, healthy tank.
What else do you feed your betta other than blood worms? Pellets? Mysis, betta flakes? Keep in mind a betta's tummy is about the size of one of his eyes so they are very easy to overfeed.
I'm sure Byron or Nick will be along shortly to tell about the compatability of your betta with the other fish you mentioned. I am not sure on the tetras but I can tell you right now a guppy and a betta do not mix, as betta will often mistake a colorful guppy as a rival and likely attack and kill the guppy. Betta do best when kept alone or in a tank with fish that won't provide "rivals" to your betta. Please know that that not all betta are the same. Some may have no issue with other fish and some will want nothing to do with anything in their tank, not even a snail.
