I also turn around in CW only because of oxygen concerns, never because of equalizing.
Once you get into this situation, there are two approaches to going deeper:
- Juggling of variables (produces fast, dramatic results)
- Hypoxic training (produces slow, gradual results within certain limits)
Juggling of variables includes:
- Modifying breathe-up (most likely switching to sub neutral breathing, very minimal amount of breathing, switching to a more relaxed breathing position, using a float to breath up, pack stretches for lung capacity, starting the dive with far more CO2 than before, etc)
- Modifying ballast amount and/or location (switching to mostly neck based ballast), optimizing ballast for fin stiffness and dive profile
- Optimizing dive profile (probably means sinking at 25-30m, aiming for 0.8-1.0m/s), optimizing monofin technique, and ascent speed & profile
- Possibly switching to either hands free equalizing or fluid goggles to allow extended arms during the descent
- Increasing cold tolerance to allow a thinner wetsuit, or better yet, no wetsuit or half a wetsuit (nothing on the legs to increase vasoconstriction)
- Increasing vasoconstriction by diving more often (four straight days of diving will do amazing things for vasoconstriction, but only if no cardio is done)
- Changing in-water warm up, or eliminating in-water warm up, depending on suit configuration, water temp and physiology
- Switching to mouth-fill equalizing at 25-30m to minimize wasted energy spent equalizing at depth
- Re-inhaling from mask on whole ascent
- Learning to relax better, both during breath-up, monofin kicking and sink phase
- Better, more efficient recovery breathing at end of dive (hook breathing or reducing number of recovery breaths with a hold)
- Purchase of a better or custom monofin to suit your style
Once those have been optimized, then, and only then, is hypoxic training the only way to progress. In my case, apnea hiking twice a week works well, but diving 4-5 days a week in cold water works even better--the problem in repeated diving is avoiding tendonitis in the feet, which is almost impossible. Another good exercise is power training using 'power bands', very cheap and effective for building fast twitch fibers.
I would say that the most important factors would be starting the dive with far more CO2, being extremely relaxed during the breathe-up, using mouth-fill equalizing, proper profile in terms on sink depth & speed, and using half a wetsuit or no wetsuit.
Note that if you use no wetsuit or half a suit, I still recommend using gloves and 'half-booties', because discomfort in the hands & feet from cold is not only unhealthy but prevents relaxation.
