I'm so sorry! How sad:hugs
Canker can be very hard to treat, you did the very best you could.
The lesions can grow rapidly and form masses that invade the esophagus, crop and sometimes the liver and brain.
Poor guy!
It sounds like he's been battling this for a long time.
If he's worsening with medications, then it may be best to stop those.
Is vet care an option.
As far as I know, the correct dose for treating Canker is below.
If you are reading give 2X a day, what's the context of that dosing and what type of bird?
Try the powder you have until you can get the tablets.
You can always make a smaller batch, the label says 4tsp powder per Gallon of water, so break it down:
2tsp powder per 1/2 Gallon of water.
1tsp powder per Quart of water.
1/2tsp powder per Pint of water.