Understanding the Components
Before you even think about clipping on that mini scuba tank, it's crucial to understand the two main pieces of gear you're working with. Your BCD, or Buoyancy Control Device, is essentially your underwater jacket. It's not just a vest; it's a complex piece of equipment with multiple D-rings, pockets, and webbing straps designed for attaching essential gear. The most critical attachment points for a pony bottle are the D-rings, typically made of stainless steel or plastic-coated metal, rated to handle significant loads. A standard BCD might have two to four D-rings on the front and sides, each with a safe working load of around 200-250 pounds (90-113 kg). The mini tank itself, often called a pony bottle or spare air cylinder, is a small, independent scuba tank, usually holding between 3 to 30 cubic feet of air. A popular and highly manageable size is the 19 cubic foot (cf) aluminum tank, which stands about 19 inches (48 cm) tall, has a diameter of roughly 5 inches (12.7 cm), and weighs approximately 12 pounds (5.4 kg) when empty. This size provides a meaningful emergency air supply without being overly cumbersome.
Choosing Your Attachment Method
There isn't just one "correct" way to attach the tank; the best method depends on your BCD's design, the size of the pony bottle, and your personal preference for streamlining and accessibility. The primary goal is to secure the tank firmly so it doesn't shift, dangle, or create drag, while still allowing you to deploy it quickly in an emergency. Here are the two most common and effective techniques:
Method 1: Using a Bolt Snap and Bungee Cord (Most Common)
This is the gold standard for a reason. It's secure, simple, and allows for quick release. You'll need a few key pieces of hardware, often sold together as a pony bottle mounting kit. The setup involves using a sturdy bolt snap—a metal snap hook with a threaded barrel—that screws directly into the tank's valve handle. The bolt snap should be appropriately sized; a 3-inch (7.6 cm) snap is common for this purpose. A bungee cord loop is then used to hold the bottom of the tank snug against your body or BCD. The process is straightforward:
- Attach the Bolt Snap: Screw the bolt snap tightly into the hole on the tank valve. Use a drop of thread-locker to ensure it doesn't vibrate loose.
- Clip the Top: Clip the bolt snap onto a sturdy D-ring on your BCD, ideally one located on the left side of your chest or waist. Mounting it on the left keeps your primary regulator hose on the right unobstructed.
- Secure the Bottom: Loop a bungee cord around the body of the tank near its base. Then, attach the ends of the bungee to another D-ring lower on your BCD, creating a tight, stable triangle of support. The tension should be enough to prevent wobbling but not so tight that it's difficult to unclip the top snap.
This method is brilliant because if you need the air, you simply unclip the bolt snap, and the tank is free. The bungee at the bottom can often be stretched and released easily.
Method 2: Using a Specialty Pony Bottle Holder
For those who want maximum security and a more integrated look, a dedicated nylon holder is a great option. These are essentially sleeves or holsters that you permanently attach to your BCD's harness or webbing. They often feature a quick-release buckle or Velcro strap. You slide the tank into the holder and fasten the strap around it. While extremely secure, this method can be slightly slower to deploy than the bolt-snap method and adds a bit more bulk to your BCD. It's an excellent choice for larger pony bottles (e.g., 30 cf) or for technical diving configurations where redundancy and rock-solid attachment are paramount.
| Attachment Method | Best For | Pros | Cons | Estimated Setup Time |
|---|---|---|---|---|
| Bolt Snap & Bungee | Recreational divers, smaller tanks (3-19 cf) | Quick deployment, lightweight, highly adjustable, minimal drag | Requires correct knot-tying for bungee, can swing if not secured properly | 2-3 minutes |
| Specialty Holder | Technical divers, larger tanks (19-30 cf), rough conditions | Extremely secure, clean look, integrated into BCD | Slower deployment, adds bulk and weight, less adjustable | 5-10 minutes (for initial installation) |
Step-by-Step Attachment Guide
Let's walk through the bolt-snap method with precise details, as it's the most versatile technique. Assume you have a 19 cf aluminum pony bottle and a standard jacket-style BCD.
- Gear Check and Preparation: Before the dive, inspect your gear. Ensure the pony bottle is filled to its working pressure, typically 3000 PSI. Check that the regulator on the pony bottle is functioning and that the O-ring on the tank valve is in good condition. Confirm the bolt snap screws smoothly into the valve.
- Positioning on the BCD: Hold the BCD in front of you. Identify a primary D-ring on the left side, around your chest or waist area. This will be your top attachment point. Now, locate a secondary D-ring lower down, near your hip or on the same side of the waistband. This will anchor the bungee cord. The tank should sit at a slight angle, with the valve (top) higher than the base, mimicking the orientation of your main tank.
- Top Connection: Firmly screw the bolt snap into the pony bottle's valve. Once hand-tight, use a wrench to give it a final quarter-turn, but avoid over-tightening. Now, clip the bolt snap onto your chosen primary D-ring. You should hear a definitive "click." Tug on it gently to confirm it's locked.
- Bottom Connection: Take a length of 1/4-inch (6 mm) bungee cord. Loop it around the tank's body, about 4-6 inches (10-15 cm) from the bottom. Tie the ends together with a double fisherman's knot or a simple square knot, leaving a loop. The loop should be just large enough to hook onto your lower D-ring with a bit of stretch. Hook the bungee loop onto the lower D-ring. The tank should now be held firmly against the BCD. There should be no noticeable play or movement when you shake the BCD.
- Final Configuration Check: Put the BCD on. The pony bottle should feel balanced and not pull you to one side. The regulator second stage (the mouthpiece) should be easily accessible with your left hand. Practice reaching back and unclipping the bolt snap a few times to ensure you can do it smoothly. The hose should be stowed with a rubber band or keeper to prevent it from dangling.
Critical Safety Considerations and Configuration
Attaching the tank correctly is only half the battle; how you configure the entire system is what makes it a true safety tool. A poorly set up pony bottle is worse than not having one at all, as it can create a false sense of security.
Valve Operation: The valve on the mini tank must be fully open before you descend. Unlike your main tank, which you check with a quick glance at your SPG, the pony bottle has no pressure gauge in your direct line of sight. Develop a pre-dive ritual: tap the valve handle to ensure it's in the open position (turned counter-clockwise all the way). A common practice is to open it, then close it a quarter-turn to prevent it from being accidentally knocked shut, though some divers prefer to leave it fully open.
Regulator Setup: The regulator on your pony bottle is your emergency breathing source. It must be protected. The second stage should have a cover or be tucked under a bungee loop on the tank itself to prevent free-flow. The hose should be of an appropriate length—long enough to reach your mouth comfortably but not so long that it becomes an entanglement hazard. A 22-inch to 28-inch (56 cm to 71 cm) hose is typical.
Buoyancy Impact: Remember, an aluminum tank becomes more positively buoyant as you breathe the air out of it. A 19 cf aluminum tank can lose over 2 pounds (almost 1 kg) of weight by the time it's empty. You need to compensate for this with your BCD's inflator during your ascent. This is a critical skill to practice in a controlled environment. Many divers opt for steel pony bottles for this reason, as they remain negatively buoyant even when empty, but they are heavier and less common.
Common Mistakes to Avoid
Even experienced divers can make errors when integrating a new piece of equipment. Here are the pitfalls to watch out for.
- Improper Clipping: Never clip the pony bottle to a dump valve leash or a flimsy accessory D-ring not designed for load-bearing. Always use the main, reinforced D-rings on your BCD's harness.
- Loose Attachment: A tank that swings or bangs against your main tank is a nuisance and a potential hazard. If there's movement, tighten the bungee cord or reposition the attachment points.
- Ignoring the Hose: A dangling hose can snag on wreck lines, kelp, or coral. Always secure the hose close to the tank body with a keeper.
- Skipping the Drill: The most dangerous mistake is not practicing its use. Regularly, in a pool or calm open water, simulate an out-of-air emergency. Practice the muscle memory of locating the pony bottle, unclipping it, purging the regulator, and breathing from it while making a controlled ascent. This drill should be as automatic as clearing your mask.