Do you run out of bottom time before you run low on air? 

You might want to consider the benefits of being a PADI Enriched Air diver.  Diving with enriched air means that you can stay down longer or have shorter surface intervals between dives.  This is by far the easiest and most popular PADI Specialty course!  It only takes a couple of hours to go over the theory and answer the knowledge reviews. After that you will learn how to analyze the contents of an Enriched Air cylinder and then you are ready to dive! 

Duration: half a day without dive

Prerequesites: To do the Enriched Air Specialty you need to be an Open Water Diver and 12 years old.