Tank Choice 101: Aluminum vs. Steel, 80s vs. 100s, and Choosing the Right Tank for Your Dive Profile

When you first learn to dive, the tank strapped to your back is usually an afterthought. You show up, the instructor hands you a heavy metal cylinder, and you go diving. But as you progress, log more bottom time, and start dialing in your buoyancy, you quickly realize that the tank you choose drastically impacts your comfort, your weighting, and the length of your dive. Buying your first set of tanks is a major milestone, but walking into a shop and seeing rows of different metals, sizes, and pressure ratings can be overwhelming.

At Cactus to Coral Scuba, we want you diving with the equipment that perfectly matches your body, your air consumption, and the environments you explore. It’s time to demystify the cylinder wall. Here is your Tank Choice 101 guide to understanding the great debate between Aluminum and Steel, and navigating the numbers.

The Heavyweight Debate: Aluminum vs. Steel

The most fundamental choice you make is the material of the cylinder. It’s not just about durability; it’s entirely about buoyancy characteristics.

The Aluminum Standard

Aluminum tanks are the undisputed king of the resort and rental market. They are relatively inexpensive to manufacture, highly resistant to external rust, and take a beating. The most common tank in the world is the Aluminum 80 (AL80).

• The Buoyancy Shift: Aluminum is a lighter metal. A full AL80 is negatively buoyant by about 1.5 pounds. However, as you breathe the compressed air out of it, the tank becomes lighter. By the time you reach 500 psi at the end of your dive, an AL80 is actually positively buoyant by about 3 to 4 pounds.
• The Weight Belt Penalty: Because the tank wants to float at the end of the dive (exactly when you need to be neutral for your safety stop), you must carry an extra 4 to 5 pounds of lead on your weight belt to compensate.

The Steel Advantage

Steel tanks are the darling of local, cold-water, and technical divers. They are more expensive upfront and require careful maintenance to prevent internal rust, but their in-water performance is unmatched.

• Consistent Negativity: Steel is dense. A High Pressure Steel tank starts off very negatively buoyant (often -8 or -9 pounds). More importantly, even when completely empty, it remains slightly negatively buoyant.
• Shedding the Lead: Because the tank never floats, you can take 4 to 6 pounds of lead off your weight belt or BCD. Moving that weight from your hips to your back radically improves your horizontal trim, making you more streamlined and comfortable in the water.

Decoding the Numbers: 80s vs. 100s

The number on a tank refers to its internal capacity in cubic feet of gas at its working pressure. But size and pressure work together to dictate the physical dimensions of the tank.

The AL80 (The Baseline)

The standard Aluminum 80 holds roughly 77 cubic feet of air at a working pressure of 3000 psi. It is a tall, relatively wide tank. For the average diver on a shallow tropical reef, an AL80 provides plenty of gas for a 45 to 60-minute dive. However, its height can be an issue for shorter divers, often bumping the back of the head or pushing down on the hips.

The Steel HP100 (The Sweet Spot)

The High Pressure (HP) Steel 100 is often considered the perfect all-around tank. It holds significantly more air (100 cubic feet) at a higher pressure (typically 3442 psi). Because the metal is stronger, the tank walls can be thinner, and the higher pressure means the air is packed in tighter.

The result? An HP100 is actually shorter and more compact than an AL80, yet it holds 25% more air. If you are an “air hog” who always has to end the dive before your buddy, switching to a 100 is an instant game-changer.

Other Notable Sizes

• AL63 / Steel 72: Smaller, lighter tanks perfect for petite divers or kids who find standard tanks too heavy and cumbersome.
• Steel HP117 / HP120: Massive capacity tanks favored by very large divers with high air consumption, or technical divers doing extended profiles. They are very heavy on land!

Choosing the Right Tank for Your Profile

How do you make the choice? It comes down to where you dive and how you breathe.

Scenario 1: The Local Arizona & California Diver

If you are diving Lake Pleasant in the winter or road-tripping to San Diego, you are wearing a thick 7mm wetsuit or a drysuit. These exposure suits are incredibly buoyant, requiring a lot of lead. The Winner: Steel. A Steel HP100 or HP80 allows you to strip pounds of lead off your belt, improving your trim and making your rig much more comfortable to carry.

Scenario 2: The “I Can’t Get My Buoyancy Right” Diver

If you constantly struggle with your feet dropping or feeling like you are fighting to stay horizontal, the buoyant shift of an aluminum tank might be working against you. The Winner: Steel. The negative weight on your back acts as a natural keel, locking you into that perfect flat trim.

Scenario 3: The Dedicated Travel Diver

If you only dive on vacation in the Caribbean or Mexico, you will be renting tanks, and they will almost certainly be AL80s. The Winner: Aluminum. If you want a tank for the pool or local summer practice that mimics exactly what you will feel on vacation, buy an AL80 so your weighting remains consistent across the board.

Find Your Perfect Fit at Cactus to Coral Scuba

Reading about buoyancy is one thing; feeling it is another. The best way to choose a tank is to get fitted for one. Come into Cactus to Coral Scuba and let us analyze your setup. We can show you the physical size differences, help you calculate the weight you can drop by switching to steel, and even set you up with a rental steel tank for your next Lake Pleasant dive so you can feel the magic for yourself.

Stop fighting your gear and start enjoying your bottom time. Your perfect tank is waiting!