Even the bigger crystals will dissolve fast. I use water softener solar salt which is a very large crystal and it dissolves almost as fast as fine grained pool salt, is often purer than some of the 'pool salt' I have seen, and costs less. If you spread it out instead of having it all in one place it will dissolve faster and keeping the pump running 24/7 until is it dissolved helps also. Salt sitting on the liner should not have any ill effects. In fact, I just get n the pool and push the stuff around with my feet when I add salt. Brushing is fine but not really necessary. POP (Pool owner patience) is more important!