Pellet salts have a problem where they break down. The pellet dissolves into a mush that does not allow water to flow through it. This can cause several problems depending on what kind of system you have.
Solar or rock salts do not have the problem that pellet salts have, but they do have theirs. Solar or rock salts will form bridges. This is where the salt gets wet then dries to form a bridge in the brine tank. This problem can be solved by beating on the outside of the tank to keep the salt broken up.
The best thing to do is keep the salt just above the water level in the brine tank (if you have that type of system). It is not nessasary to keep the tank full. This reduces the mush problem of the pellet salts, and stops the bridging problem of the solar and rock salts.
What kind of system do you have?