Based on experience I have to say you should "air" your pool for 2 hours a day minimum while running the pump. If you miss a day, give it an extra 2 hours. If you leave the solar cover on indefinitely, you WILL get chlorine lock within a week, then algae will set in.
2-4 hours of "breathing" allows the chlorine that is eating algae (the chlorine that makes the pool smell) to gas off and leave only the free chlorine in your pool. Some think it keeps their chlorine in the pool longer, in a way it does, but it also keeps the wrong chlorine in your pool which is a bigger problem.
FUI - just because your pool is clean and clear, does not mean you have chlorine in there "waiting" for contminates, it is a continuous cycle without rest, ther chlorine is ALWAYS fighting something whether you can see it or not, I find if you can see it you're on your way to a problem, so keep it where you can't see it.