I have the utmost respect for Sakura, and I believe she gave you excellent advice. However, I'm going to respectfully disagree with her on one point.
The high pH of your water will cause a high level of ammonia
, rather than the safer ammonium.
At low pH, more ammonium is present. At high pH, more ammonia is present. (Here is an article that describes the process: Surface Waters: Ammonium is Not Ammonia
Therefore, I think you need to tackle two issues:
1) The ammonia level of your water.
2) The SBD issues that Buzz is dealing with.
As for why it's only affecting Buzz: I don't know anything about Rasboras. Is it possible that they're less affected by ammonia or pH levels than Bettas? If so, this would explain why only Buzz is affected.
1) Dealing with the ammonia issue:
I think this may be perhaps the most important component. Can you get some bottled drinking water? Look for one that says "Minerals added for flavor." These minerals are electrolytes that are needed to maintain good health (in people, as well as fish!).
There are many ways to do acclimate your fish to a new type of water. This is one way. If you have a method you prefer, you can definitely use it. It may be easier to treat him in a small container/tank/bowl for this, such as the breeder box you have him in:
- Note the temperature of the current tank water.
- Use bottled water that has "minerals added for flavor." (You should be able to get 1 gal jugs of this.) The water should be at the SAME temp as the tank water (within 2 degrees F / 1 degree C is OK).
- Be sure to add the correct amount of water conditioner.
- Since he's currently in Epsom salt (2 teaspoons/gal), add this same dosage to the new water. Be sure to stir/shake until the salt is completely dissolved.
- Remove about 25% of the water from his hospital tank.
- Replace this water with the bottled water mixture.
- Wait at least 15 min. (More time is OK!)
- Repeat the 25% water change process another 3 times. Be sure to wait at LEAST 15 min between changes.
- Tomorrow, do one 50% water change.
If the ammonia and/or other nitrogen-containing compounds are what's causing his problems, this should help.
Another way to lower pH slightly is to add a tannin source, such as dried IAL or oak leaves. Tannins are slightly acidic, which will help lower the water pH. They also have some soothing and antimicrobial properties, which may help him.
Put some plastic food wrap (Saran, Glad, etc) over the top of his tank. Be sure to leave several inches of air so he can breathe. The wrap will increase the humidity, and make it easier for him to breathe.
2) Dealing with Buzz's SBD symptoms, if they continue:
If the new water doesn't help improve his symptoms with 24 hours, I would increase the Epsom salt dosage by 0.5 teaspoon/gal every 12 hours until you're at a final dosage of 3 teaspoons Epsom salt per gallon:
Ie: Current dosage: 2 tsp Epsom salt/gal. After 24 hrs, if there is no improvement, increase this to 2.5 tsp/gal. Wait 12 hours, assess the situation. If no improvement, increase to 3 tsp/gal.
Also, if he doesn't improve within 24 hrs of being in the bottled water, I would start to look at medications.
As Sakura mentioned, Kanaplex would be an ideal antibiotic. It's broad spectrum, meaning it's effective against many types of bacteria. And it's able to treat internal bacteria.
JadaBlu had some success using tetracyline. It's also a broad spectrum antibiotic. She soaked the pellets in it, so that it acted internally. You may want to PM her to find out more about this. (Or do a search for her posts.)
Has he pooped recently? Did it look OK? If not, this could be a sign of internal parasites.
(It's 3am here, so I hope this post is coherent!