I'm not sure what time it is where you are but it's early morning here in the states. I'm sure someone will be responding to your post in a few hours when everyones awake. There are great people and great help here, no worries.
The very best and easiest fungus clear medication I have found for bettas is Furan-2. It does not affect the biological filter and is fairly easy to use.
Before adding any medication to the tank remove the carbon filter from the filter!!!
DAY ONE: Use 1 capsule for each 10 gallons of water or if you have less than 10 gallons dissolve one capsule in 10 tablespoons of water and use 1 tablespoon for each gallon of water.
DAY TWO: Use another dose the same as the first day.
DAY THREE: Do a 25% water change and add another dose the same as the other 2 days
DAY FOUR: Do another dose the same as the other days.
DAY FIVE: If the problem is cleared up, do another 25% water change and put the carbon filter back into the filter to remove the rest of the medication; IF the problem is stil there, start at DAY ONE and repeat all FOUR days of the treatment over before doing the DAY FIVE . If you have any questions, please ask before adding medications.
This medication is available at some petstores and is in packets (cards) of 8 capsules so is good for 2 rounds of the medication and should be enough for any case of mouth fungus.
If you cannot find it, the second choice is; Jungle Labs Fungus Clear Tank Buddies
DAY ONE: You use 1/2 tablet per 5 gallons of water and drop them in the tank and they fizz to dissolve.
DAY FOUR: You leave them in the tank for 4 days and then change 25% of the water and repeat the dose for another 4 days. Then do another 25% water change.
DAY FIVE AND DAY NINE: It also needs to be repeated for another course of medications for 8 days like is mentioned in the first two days.
DAY 10: Then you do the final 25% water change and replace the carbon filter here too as you will have removed the carbon from the tank here also. This is a bit more available but will turn your water and suction cups green. The other things will look green but will clear up when they are back to clear water for a few days. It also takes a while longer to work.
Please do not put as much food in for your betta during this time as he will have a sore mouth and it will painful to eat so he will not feel like it. Just a pellet 3 or 4 times a day. or a blood worm 3 times a day. will do okay. I hope this helps.
Welcome to our Board and we do welcome your Betta too and as AesSedai has asked if you could let us know his name it would be appreciated here. We address them by name as they have such a personality and are the reason for the board that we feel it is only fair to give them the honor to allow them to be known by name. We are here for you and will try very hard to help you get your little one back to the pink of health.
Oh, I am so sorry about Yocko. It is always so hard to lose a betta as they are so filled with personality. :'(
I am afraid that the fungal infection could indeed be carried by the shrimp to the other tank as it is caused by a type of parasite that is transferable to other fish and the shrimp may very well carry it to the other fish. It would still be worth treating the tank with one of the medications that I mentioned and then it would probably be safe for other fish or for the shrimp to be transferred as he will have been treated for the disease. The tank should not have to be disinfected further then either. It should be safe for other fish when you decide to add them. The directions for treatment need to be followed to the letter after removing the carbon from the filter and the best temperature for the medication to work at is about 82 degrees F/or 28 degrees C as I do not know where you are writing from exactly and what temperature system you use.
I do thank you for the compliments. We are indeed a fine and good forum and try very hard to help those who come to us. We do our very best to give information that is going to keep the fish alive and healthy. It is so unfortunate that we are sometimes not able to do so and we do grieve with the ones who lose their fish. If there is anything we can do to help you please do not hesitate to let us know. You have my deepest sympathies.
Welcome to the forum and please do feel welcome to stay with us. Ownership of a betta is not a requirement to stay with us. You are welcome to stay and browse through the forum or check on information about the other fish you own or any you may want to own in the future. You are welcome to comment and ask any questions you may have and we will do our best to help you.