As always, when I return home, I will take a look at my precious fry. Then I notice something about 1 of the 3 tri-ban butterfly which I removed from the community tank 3 days ago.
FIN ROT! And a very bad case of fin rot for this fry, I must add. This is weird considering that the fry in the community tank are all healthy and well and free from disease. Never mind the cause, the matter at hand calls for an emergency.
Immediately (and I mean immediately, with wallet, phone and all the nonsense items still in my pocket) I did a 100% water change. Add 1/2 teaspoon of aquarium salt, 100ml of new Ketapang Extract and proper dosage of OceanFree External Fungus and Bacteria Away. Of course it will be best to shift them to the shelf with the aquarium light, and that's what I did. I then look at the other 2 tri-ban butterfly and realized that both of them got a minor case of fin rot. Did exactly the same treatment for the two of them. With the treatment for fin rot given, I can now only wait and see if there's any improvement.
The next step will be to check every single jarred fry for fin rot with a flashlight. Fortunately all of the bettas are healthy and well and free from disease. I suspect that the fin rot might be caused by an expired batch of ketapang extract. It was the last bit of the extract and it was full of sediment. I tend to give a heavier dosage of ketapang extract during jarring, therefore only the 3 newly jarred fry suffered from the contamination, while the rest (with normal dosage) are unaffected. Well, learn from my mistake, if you are near the last bit of ketapang extract, discard it and start a new batch.
Note: The extract was about 2 month old, I am guessing that towards the end when there are very little amount of extract in the container, the extract starts to expire rapidly (because of the increased volume of air in the container), causing a boom in bacteria. So it is wise to filter and transfer your reminding extract to a smaller container to extend the shelf-life.