Pool Stores sell salt specifically branded as pool salt. What is pool salt ? Is it any different that normal salt ?
The answer is NO. Salt is salt. You need to be careful though because some salt is not just salt.
Table Salt (used for food) usually contains sodium chloride and is referred to as Ionized Salt. This type of salt is not pure salt and is not good for salt chlorinators.
Ice Salt (used on the road) is very cheap salt and is not pure. It contains other mineral particles and is not good for salt chlorinators.
Water Softener Salt (used in home water softener) is pure salt and is perfectly fine for salt chlorinators. The only thing about this salt is that it comes in small pellets of about 1/4" tick by 1/2" long. It is a bit longer to disolve in the pool than the fine grain pool salt, but is much cheaper. You will often pay half the price for the water softener salt compared to the pool salt. The pellets are really not an issue. It will usually dissolve within an hour or two, and you need to wait that time anyway because the chlorinator salt measurement takes about 24 hours to adjust.
Another thing: It is totally useless to try and dissolve the salt in a container with hot water. Doing so, you try to dissolve the salt in a fairly small quantity of water and the solubility will be reach very quickly and you won't be able to dissolve much salt. In other words, there is a maximum amount of salt you can dissolve in a given quantity of water, so it's better to dissolve salt in a very large quantity of cold water than in a very small quantity of hot water.