Divers who dive with Enriched Air, also known as NITROX, understand the benefits … increased bottom time. This academics-only class can be completed in one mid-week night from 4:30 to 8:00. It will teach you all you need to know to safely dive with blends of O2 up to 40% which can extend your bottom time by 15 minutes or more. This certification is especially helpful in depths from 60′ to 120′. If combined with Advanced Open Water, there is a $50 discount.