One day every month or for a day in every month?

I am an online seller at Amazon and I will put a note on my product. But how to create this sentence I am not 100% sure.

Ventilating one day every month will extend the life of the product.
or
Ventilating for a day in a month will extend the life of the product.

or how should I make this sentence in other way? I want to say that customers should ventilate the product one whole day in every month. Otherwise the product gets mold.