A: Ahhhh... Nothing like a really broad question to get my day (and week) started :)). I am afraid you gave me very little to work with Catia. You did not describe any 'visual' symptoms, other than the fact that he is not active. You say he is showing "signs of a bacteria infection or parasites" but did not describes the signs. What signs is he showing? (other than laying at bottom). 

If one does not know what is wrong with a betta, how is one to know how to treat it? In other words, if your betta is acting sickly, how can you figure out what's wrong? Usually one of four things could be happening: Your betta could have a bacterial infection, a parasitic infestation (and sometimes both), fungus or poisoning. 

The parasitic infestation is the easiest one to spot because it has obvious external signs. So I would check for it it first. Then I would check for fungus (usually also easy to see), then poisoning, then last but not least possible bacterial infections. By the way this check list is not sorted by degree of seriousness or even by degree of probability. It is sorted by degree of obviousness and designed to allow to work from an easy to figure out process of elimination. 

• parasites: can be easily spotted with a flashlight. If white spots can be seen (about the size of a grain of salt), then you have ich. If a golden powdery layer can be seen covering the scales, especially on body and the base of fins, then you have velvet. Of course there are many other parasites, but these two are the most common betta pests and you will rarely deal with anything else. Possibly an anchor worm now and then, but bettas usually do not act sick when they have one on them (you can see them they look like tiny whitish strings hanging down from the betta's skin - often the gills). If you cannot see any of above, then you are safe assuming that your betta does not have parasites. So then no need to give it parasite medication! Proceed to the next item on the list.

• fungus is also easy to spot because it is also external. It will look like 'stuff' on your fish (cotton like growing stuff, slimy stuff, etc...). Just think old food in the fridge kinda stuff (yeah, I know you all have a black belt in fridge experiments LOL). If however you see nothing at all on your fish's body or fins then you can proceed to the next item on the list.

• water quality. Water is often the culprit when bettas start laying at the bottom and looking terrible. So you should also scrutinize your water as a potential problem when your bettas are not doing well. Are your nitrite and ammonia levels within safe range? Did you test? Is your water CLEAN? Is your filter working well? Also make sure the water is properly treated, make sure nothing toxic got in it (soap, windex, bleach, etc...), make sure your city is not having problem with their tap water, or that your building does not have old copper pipes, etc... If in doubt, you might want to get bottled water for a while and see if that helps. Remember switching waters must be done the proper way!! Or you could kill your fish. (see link). If your water looks fine and other bettas in same water are doing great, then your water may not be to blame. So then then you can proceed to the next item on the list.

• bacterial infections can sometimes be easily spotted (red sores, rotting fins that fall apart, lesions, etc...) and most often come from poor living condition (especially dirty water). But sometimes they do not have outside signs and are more difficult to spot. So in doubt, always treat with a very broad spectrum antibiotic. I recommend spectrogram or kanacyn by aquatronics  if you can't find the first.

The above should help all of you go down some sort of "check list" when you are trying to play betta doctor. It will help you narrow it down and treat with the proper medication right away. The whole "Let's try every medication I have in my betta drawer" approach can do more harm than good because it stresses out your fish unnecessarily and while you are trying drugs that won't work, the disease is progressing and flourishing! So beware. Once you have properly figured out the problem, you can look in my betta diseases section for the right cure.