Where can I buy 12 pound of baking soda? I have been told it helps to keep swimming pools free from algie

They use it all the time in the USA it makes the water crystal clear

Ask around for a wholesale catering supplier.

You can get little tubs in most supermarkets but you'll need a lot of those. Bicarbonate of Soda and Baking Soda are similar. There is a difference that I'm sure someone can tell you but I would imagine that both would be just as good for a pool.

Hi -- Sodium Carbonate is available in 5 kg packs from the suppliers on ebay, just put item number 200170900735 into the search box on ebay. If they are not exactly what you want contact the seller because they do advertise up to 25 kg bags available.

Baking soda is pure sodium bicarbonate.

Baking powder contains sodium bicarbonate, but it includes the acidifying agent already (cream of tartar), and also a drying agent (usually starch).