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Had some pretty unnerving issues this last dive. By dive 7 I had worked out my buoyancy and trim; it came very easy to me, I did a proper weight check, etc.
Today, when my tank got to about 1500 psi I could not stay down, I had to fin hard to keep depth. I've dived in the exact same conditions the past three times with no trouble staying down at the same depth with 500 psi. Spring water, 5mm suit, no weight, steel lp 85, zeagle express tech BC.
Near the end of the dive, I became very nauseous. As I write this 5 hours later, I'm still kind of nauseous with a headache.
The only physical explanation I have for the buoyancy is that there was trapped air somewhere. I kept the valve as high as I could though.
Feeling sick must have something to do with my ears, which felt fine the whole time. I don't think it's possible I have DCS.
Sounds like you might have a little more work to do on your bouyancy....
There may have been air trapped somewhere in your BC or your wetsuit. Or you may have been overfilling your lungs. The nausea may simply be from over exertion. Finning "hard" to stay down will do that to you.
Well a 1000 psi in a LP 85 is about 2 pounds of weight or about a liter of displaced water. Try putting on a pound or two more and trying it again. A lot of people do not have it shorted out to a pound or two until dive 50. You're doing fine. Do be aware of your breathing patterns. That is easier said than done, since a lot of that can be unconscious reactions to stress. It sounds like you may have had some of that during the dive.
I can only suggest one thing with the BC since i dive dry and only did like 4 dives in a wetsuit. i tend to roll onto my side when i let air out of my BCD to make sure that there is no chance for air getting "stuck" in the BC.
One thing I found out when I started to go up when i didn't want to was I always took a big breath (not holding it). I've seen this with a few other divers and its something you have to force yourself not to do (it makes things worse). so when you feel like an unplanned ascent is happening breath out(and breath shallower for a sec) and adjust your BC.
Also you might have as others said over did it finning and got a bit of a CO2 hit which will die down overnight. If not you might want to see the Doc just to be safe. If you have to wear an extra lb or two there is nothing wrong with that. Also have you done your weight check at the end of a dive. Thats when you'll need the most weight to make up for the difference in tank buoyancy characteristics.
As others have said, it sounds like C02 from over-exertion. Take it easy, and keep "working" on buoyancy and trim. With 7-9 dives under your belt you don't have enough data points to know whether you've "worked it out." After nearly 500 dives I still work on these two critical aspects on every dive. In diving, the moment you assume you've got something "worked out" will probably be the moment you find out you're wrong.
Any chance you had some other "weight " with you on the earlier dives? Accessories like lights that you didn't take this time? Everything we bring is a + or - in the buoyancy equation.
If you were other wise working or anxious when staying down became difficult it could easily go as you describe.
Keeping the valve (inflater valve?) high is a good start but some BCs want to to tip so that side of the bladder is high too. Otherwise some air can hide in the right shoulder. This is especially true if the rig got to ride up off your shoulders some.
We you feeling nauseous before the difficulties started,? (It sounds that way) You say spring, was there an current or off particulate movement? Sometimes we can see things moving in the water that are counter-intuitive. The brain can't figure it out and goes TILT. If it happened afterwards and you worked hard to save the dive that could do it too. If you go to the point of hyperventilating you probably retained CO2 and that can leave you feeling like crap. Did you get a headache?
Was it the same LP85 for all dives? It looks like the are all very close in buoyancy properties but you never know.
Baring an AH HA moment I would bring a few extra pounds next time just to be sure. A few extra won't cause any harm. Put it where you can remove it and you can hand it to your buddy near the end of the dive to confirm the need.
As the other posts point out, look for the variables in dive 9 that made it different from the other 8. Exertion, your own body weight, how much time between dive 8 and 9, what you ate (nausea related to gastric gas?), activity, other accessories carried, and so on. Also, were you wearing the same wetsuit as before? Not all 5 mil suits are "equal". Also, any changes in other equipment from earlier dives? By logging details of each dive, the variables can be identified and appropriate correctionmade. Happy Diving!
I don't mean to say that I have my buoyancy perfect after 8 dives, but the degree to which i was positively buoyant felt extreme given previous experience. I'm going to redo the weight checks in my parents swimming pool. Tipping the right shoulder down did not occur to me and it should have. I'm no longer nauseous this morning. This was at paradise springs in ocala. It was pretty dark (even with my light) and the cavern is gigantic, so I think working hard in the dark without much reference made me sick.