Pool Chemicals/testing Kits - Korat

My swimming pool is just being finished and although the builders supply a starter kit of chemicals I need to find a local supplier. Does anyone know of a supplier in the Korat area especially if they sell in 20/25 kg loads.

I read somewhere that there are two types of chlorine, one being in powder form and the other granules. I seem to remember that one form is better to use in hot climbes due to the lower evaporation rate. Any ideas although having said that, I well understand that this is Thailand and its on a take it or leave it basis.

Hope someone can help.