If you have access to a supplier of swimming pool chemicals, which includes many hardware stores, you can get pHPLUS that is used for raising the pH of pools. It is 98% sodium carbonate, the rest inert. I heated some to see if it would change weight and it did not. I have been using it ever since as anhydrous for my photo grade carbonate. It is about 1/5 the cost of what you would get at a photo store or even Pfotographer's Formulary.(posted 8319 days ago)Pat Gainer