When sodium ions enter the cell, water exits to maintain fluid balance?

No, when sodium ions enter the cell, water does not exits to maintain fluid balance.

Explanation:

When Sodium ions are concentrated in a higher level in the outer layer it tends to push the Sodium ions into the cell.  If three Sodium ions go out of a cell two potassium ions enter the cell. The water always accompanies the movement of Sodium ions.

The cell to perform work requires this transfer of ions. This is also useful for the nutrient absorption.  So When Sodium ions enter the cell, water does not exit to maintain the fluid balance.