This is a bad experience I had when I took my PADI open water course.

During my first dive in the swimming pool I found that I could drop to the bottom by letting the air out of my vest without a problem. But I had a very hard time staying at the bottom. The instructor tried to help me breath properly but I kept floating upwards. The instructor became impatient with me and finally added 4 more pounds to my weight belt. This did not help.

Needles to say when I got home that night I was very stressed. I did internet research on buoyancy and when it came time to sleep I found myself breathing like as if I was under water.

After a sleepless night wondering why I was the only one that couldn’t stay down, I went for day 2 of my course.
Because we were 12 students in the pool a second instructor came to help us. Then came the time to go down. I sank like a rock; however, after 5 minutes or so, I started to rise to the surface once again. The second instructor ask me to empty my BCD. I did and dropped down at once. His experience led him to conclude that my rented BCD was defective and was filling up with air on its own.

The first instructor that was impatient with me looked pretty stupid because he made it clear to the class that we should be happy that we had him because he claimed to be the best instructor in the dive center.

The very next day I complained about the rental equipment and purchased all my dive equipment, at a discount, so that I would never experience this again.

The lesson in this is purchase your gear if possible. Imagine if this happened at 30 meter.

12 students to 1 instructor sounds bad to me. I think 4 seems more standard and better to me, but I think it varies where you go. a good question to ask before you book though. My other half got 1 instructor and 1 divemaster to help on most of her open water course and got extra pool time just to practice her buoyancy (she isn't that bad honest ).

I think a lot of rental dive kit get used and abused. I had a leaky pressure gauge on my OWD course, but managed to get it changed before doing the open water part. Even with all the attention my other half got she still had issues with the BCDs she was given and was much happier when she got her own. I'd definitely recommend getting your own kit when you can afford it if you plan to do lots of diving..

Your instructor should have noticed the BCD was filling up and disconnected the inflate hose.

When I did my CCR course, I was happily swimming down to 20m when I needed to top up my drysuit - used for buoyancy instead of BCD. As I did, my instructor held up a card with an emergency scenario, I had to act on it. Before I could act on it I had to disconnect my drysuit inflator as the valve had stuck and was inflating my drysuit rapidly. So the scenario was, disconnect drysuit hose, dump excess air from drysuit, close CCR loop and bail out to open circuit as fast as possible.

It was my drysuit and it was the first time the valve had ever stuck, it was a fairly new suit but had done a lot of dives. So the moral is, even if you own your own gear, it can still go wrong. I serviced the valve and found there was a small shoulder worn into the button which would cause it to stick in a certain orientation. Flattened down the shoulder and it's never happened again, although I do dismantle it and re-grease it quite often.

Wow that sounds complicated.

I don’t know much about dry suits, how do you fill it up with air to go back up if you unplug it? Especially if you need to make a safety stop.

Komodo wrote:

It's the same as a BCD, you do not add air to ascend, you dump air as it expands. If you're neutral at the bottom a small kick upwards and you'll start ascending.

On ocassion I have known people to forget to actually fit their drysuit inflator hose to their regs, I even did it once after coming back from holiday. You just borrow your buddies at the bottom to get neutral then you don't need it anymore.