One quicky way of knowing if you need to replenish your electrolyte. Drink Gatorade.

If it tastes sweet, you're low on electrolyte, drink more up to date sport drink: Cytomax, Accelerade, Gu... or eat banana, orange, boiled red potato with the skin...

If it tastes salty, no need to drink sport drinks or take additional salt.

Smilingcat