I have sent off an email to interpet, hoping to find out what the ingredients are in this Liquisil General Tonic . From everything I have seen online about it, I can find nothing about it that would lead me to believe this could be useful in treating an active infection in a fish. This appears to be some type of water treatment to help control levels of bacteria and such in the aquarium, which is a big difference than treating a sick fish. I'm waiting to see what interpet can give me for a list of active ingredients.
As for what to do for your situation, the medication I'm going to suggest is called Furazone Green.... which is a combination of Nitrafurazone and furadolazone. This is sort of harsh for a medication, but I think your fish's condition warrants it. Besides treating the tank (follow all directions of treatment) I would suggest treating the food. Take a small amount (5 days worth) of food and put it into a small zip lock baggie or glass container, add a very very small amount of the furazone green to the food (the furazone green should be a powdered medication) and give the medicated food to the fish once/day for 5 days.
When treating the tank, 2 notes... first, if you read the directions you will see you'll only treat the tank water every other day for a total of 3 treatments. Even though the water is only being treated every other day, continue the feeding of the medicated food every single day for the full 5 days... and 2nd, when you mix the medication, use a small disposable cup or glass container (something you won't intend to use for food or drink for human consumption) and measure the powder into the container. Add a small amount of tank water to the cup of medication to completely dissolve the powder before
putting it into the tank. Once the powder has dissolved, then dump this into the tank, rinsing the cup/conatiner in the tank water at same time. The furazone green will
stain your water, so when medicating is finished you will need to do water changes and add carbon back into the filter.
Please complete the current treatment, the new medication can be mixed in safely. Between these 2 medications, I would expect to see some type of relief soon. If you notice any big changes in behavior or if more symptoms appear, please stop using the meds, do a 25% water change, and PM me for help. I have never seen a betta react badly to the furazone green, but there can always be a first time.
If you have questions, either post them here or PM me at anytime. I try to check my inbox at least once/day, sometimes more.
Best of Luck to you!!!