Back mount pony bottle

[GiraffeMarineSalvage]

Air is just fine. You are only going to use it when something has gone really wrong so no benefit to nitrox.

I don't disagree that given the short amount of time involved for a NDL ascent an air filled pony bottle is likely to be ok, but given how much EAN can impact deco obligations and what may be a faster than optimal ascent I would strongly prefer pony to have same mix simply for piece of mind given the grey areas involved in decompression sickness.

 

[johndiver999]

I don't disagree that given the short amount of time involved for a NDL ascent an air filled pony bottle is likely to be ok, but given how much EAN can impact deco obligations and what may be a faster than optimal ascent I would strongly prefer pony to have same mix simply for piece of mind given the grey areas involved in decompression sickness.

Trying to match the pony and main tank in composition means it needs to be adjusted every time you use a different mix. If that happens very infrequently, then no big deal. If it happens a lot, then you spend a lot of time and money adding and dumping gas from a pony bottle - which will probably never get used!

I top mine off with whatever tank I have on had and generally try to put the least rich mix in the tank. Using air makes things much simpler and I prefer to use air when available.

 

[Fishdip]

I don't disagree that given the short amount of time involved for a NDL ascent an air filled pony bottle is likely to be ok, but given how much EAN can impact deco obligations and what may be a faster than optimal ascent I would strongly prefer pony to have same mix simply for piece of mind given the grey areas involved in decompression sickness.

You would have 0 deco obligations if you are staying with in rec limits tho?

 

[GiraffeMarineSalvage]

You would have 0 deco obligations if you are staying with in rec limits tho?

True. But the rec limits are based upon going up slowly and generally a minimal "safety stop," both of which might not happen when using a pony bottle. Since some people get the bends after following all the rules (even though that is rare...) I personally like increasing safety margins if and when practical.
Johndiver999 brings up a very valid point of unnecessary costs if you chose optimal mix for a given depths and matched your pony bottle to that mix, but despite my not personally being a GUE diver I'm a huge fan of the standard gases they recommend for given depth ranges...

 

[happy-diver]

Yes carry some type nitrox in your pony for less nitrogen ongassing
paying attention to spg, enabling you to extend your stop if desired
without having to wonder how long before you feel a sudden clunk
from your completely empty regulator

 

[SlugLife]

We talk about "trust me" dives in a negative connotation. Trust me dives are bad. The reality is any non self redundant dive is a trust me dive. All of the agencies teach trust me dives from the very beginning of confined water.

I'm unfamiliar with this term. I'm guessing it means "Trust me, I won't put you in danger, and will be there to rescue you in an emergency?"

IMO, a safety-minded diver treats insta-buddy-dives as "a solo-dive with a buddy-hazard" and recognizes there are many scenarios where their buddy may be unable to assist.

Air is just fine. You are only going to use it when something has gone really wrong so no benefit to nitrox.

Trying to match the pony and main tank in composition means it needs to be adjusted every time you use a different mix. If that happens very infrequently, then no big deal. If it happens a lot, then you spend a lot of time and money adding and dumping gas from a pony bottle - which will probably never get used!

I top mine off with whatever tank I have on had and generally try to put the least rich mix in the tank. Using air makes things much simpler and I prefer to use air when available.

^ Basically this. I top-up my pony from my main tank each dive, and there's no (meaningful) benefit to having nitrox in an emergency-only pony tank intended for recreational depths. The transfill setup also offers the advantage of being able to practice switching each dive, taking a few breaths, and leaving the cylinder open. And if I top up a pony with a couple-hundred-psi of nitrox, once or twice, I won't lose any sleep over it.

If you start getting into technical/deep, then you'd plan your redundant-gasses, such that you could safely surface in the event that any tank or regulator failed. At that point, it's usually no longer called a "pony bottle", you're probably looking at 30-or-more cu and much of the previous discussion in this thread become inapplicable.

 

[bradlw]

that, & I would add that the MOD is fuzzy anyway....it's based on a particular PO2 target and you can go with a higher PO2 for the calculation and get a larger MOD number
so
on the question of Nitrox I'd prefer to have Nitrox on board for the added safety factor...emergency and the elevator is going up...maybe a little faster than ideal, etc... + in the even of a DCS situation the faster you go on O2 the better and going on Nitrox for the elevator ride up is just a little closer to O2 than air.... if that makes sense

 

[MaxBottomtime]

How often are you people using a pony if you have to top it off after every dive?

 

[Boarderguy]

How often are you people using a pony if you have to top it off after every dive?

Every dive I take a few breaths off mine before I splash to ensure it's functioning. I also check pressure before I leave the house. Both of those actions add up over a few dives and need for the bottle to be topped back up from ~2800 to 3000-3100. Any use during the dive for muscle memory also depletes it. Transfer whip saves time. My lds tops off no charge as well if I remember to bring it with me.

 

[BlueTrin]

@Ross19966 if you sling it like a stage, you can also put it on a short hose and hold it bent backwards against the stage. Whether you can do it easily and how to do it depends of the first stage.

Here is a pic (not mine) of someone doing it.