Buying Your First Scuba Tank

by Harry Averill:

So…you’re ready to buy your first scuba tank. That’s great.

But, before you do, there are some questions you’ll want to answer to make sure you are spending your hard-earned money as wisely as possible. These include:

• Is this the right time to be buying a tank?
• How many tanks do you need?
• What size tank is right for you?
• Should you go with steel or aluminum?

The answers to these questions will vary depending on who you are, where you live and dive, and on the type of diving you anticipate doing.

Let’s take a look at each question in greater detail.

Is now the time to buy?

Although scuba cylinders are often among the first purchases new divers think they need to make, they may well be among the last.

Remember that it generally costs little more to rent a tank than it does to get one filled.

If you do most or all of your diving at destinations you can only reach by air, you’ll not only find it impractical to travel with scuba cylinders, but also discover that use of both tanks and weights is included in your dive package.

Keep in mind also that, unlike other more personal pieces of dive equipment, comfort and fit are generally not issues when renting scuba cylinders.

For most divers, there are several other equipment purchases they should make before investing in cylinders. They include:

• Mask, snorkel and fins
• A personal dive computer
• Comfortable and adequate exposure protection for local diving
• A complete scuba system, including BC and regulator

For most of these items, comfort, fit and familiarity are essential, meaning you are better off with equipment you own, rather than unfamiliar rental equipment that may not fit properly.

That having been said, depending on circumstances, there may be compelling reasons to own your own cylinders, instead of continuing to rent. These include:

• The right size cylinder for you is not readily available for rental.
• Your dive center is still some distance away, making that additional trip to return rental cylinders expensive in terms of both time and travel.
• The satisfaction of simply owning all of your own dive gear.
• The overall convenience of not having to rent anything.

How many tanks do you need?

For most divers, a typical day of local diving involves at least two dives. For example, the most common type of dive charter is a two-tank boat dive.

This is why most divers will want to own more than one tank. Doing so will save you the inconvenience of renting a second — or even a third — cylinder.

What size tank is right for you?

By far the most common cylinder used by recreational divers is an eleven-liter aluminum model that holds nearly 80 cubic feet of air or Nitrox at its rated pressure of 2,000 PSI or a little more than 200 bar.

Among the reasons for its popularity is the fact that this tank provides adequate bottom time for most divers, without putting them at substantial risk of no-decompression limits.

However, just because a particular cylinder may meet the needs of most divers doesn’t mean it meets the needs of every diver.

For example, many younger or shorter divers find the “standard” 11-liter Aluminum 80 to be uncomfortably tall. For these divers, a shorter cylinder, such as the 9-liter Aluminum 63, may be a better fit while providing more than sufficient gas.

The flip side of the coin are those recreational divers for whom the most common cylinder sizes fail to provide sufficient gas.

Larger divers, for example, tend to have gas consumption rates that are in direct proportion to their size and, as a consequence, may prefer cylinders which are more in line with their height and weight.

Divers who spend considerable time in deeper water may also want the added safety margin larger cylinders may afford.

It’s important to understand, however, that the largest aluminum cylinders currently available are 13-liter Aluminum 100s.

If you need more gas than this, it may be time to consider a different type of cylinder, which leads to the final question you need to ask:

Should you go with steel or aluminum?

Opinions vary on which is better. It really depends on circumstances.

To better decide, you need to understand the fundamental differences between steel and aluminum cylinders.

Steel cylinders are available in a wide variety of sizes. There are steel tanks with largely the same capacities as the most popular aluminum models, as well as ones with substantially larger internal volumes, such as a 19-liter monster capable of holding nearly 150 cubit feet of gas at a rated pressure of more than 3400 PSI or nearly 240 bar.

As steel is a heavier metal than aluminum, steel cylinders tend to be heavier under water, yet may weigh less on the surface, due to their thinner walls. Divers who use steel cylinders generally need to wear less weight than divers who use aluminum tanks.

Aluminum cylinders tend to have more metal at the bottom, as this allows the tanks to stand upright without a tank boot. This can tend to make divers more tail heavy. In contrast, divers often praise steel cylinders for their excellent fore-and-aft balance characteristics.

By far the biggest difference between steel and aluminum cylinders is this: Steel cylinders can rust; aluminum cylinders can’t.

Moisture that gets inside an aluminum cylinder may cause only a minor amount of oxidation or scale and will not likely cause any permanent damage. Even salt water getting into an aluminum cylinder will not cause significant corrosion.

In contrast, even a small amount of fresh water getting inside a steel cylinder can cause a significant amount of damage if not caught in time. With salt water, the corrosion occurs even faster. If left unchecked, the resulting oxidation and pitting can damage a cylinder beyond repair.

Epoxy-coated steel cylinders can also trap moisture between the exterior coating and the tank wall, leading to unseen tank damage.

If you do a substantial amount of diving in salt water, and aluminum cylinders are available in sizes that will meet your needs, you may be better off sticking with aluminum.

On the other hand, if you dive mostly in fresh water, or you need the additional capacity, better overall balance or more compact size — and can provide the higher level of care and maintenance these cylinders require — you may be happier with steel.

Your local SDI Dive Center can help you weigh the variables and decide which is the right choice for you. To find your local SDI retailer, just visit www.tdisdi.com.