My Scubapro MK 20 & G500 Froze Up For The First Time

[rsingler]

I really don't understand all this technical detail as my top of mind question is still --- do I need to get a new regulator?

I'd give it one more try after a service and setting IP at the low end of spec. Your reg should do just fine at those settings.

But if it recurred in cold water after that, well, there are better cold water regs that can be used in warm water too. The new Mk19 from Scubapro is the sealed diaphragm equivalent of your Mk20 that would be perfect for both environments.
And there are many other sealed cold water alternatives out there, as a search of other threads will reveal. They are often a bit less expensive than Scubapro.

 

[rhwestfall]

I'm not overly concerned with 18 degrees C and that regulator set. That being said, I have much different equipment for the 3-7 degrees C I routinely see below the thermocline in the same region you are in.

A hot tune is not going to be happy in cold water... that is probably your issue

 

[halocline]

A question. I read here that for cold water it is recommended to lower the IP.
I suppose that doing this improves the situation for the second stage, but make it worse for first stage.

This is theoretically true, although the amount of theoretical increase in adiabatic cooling at the 1st stage is more than offset by the slower flow (and smaller pressure gradient to a lesser extent) at the 2nd stage.

Lowering the IP for cold water use was never about the pressure differential, it's always been about slowing the flow through the 2nd stage, especially in a purge or free flow scenario.

 

[halocline]

I really don't understand all this technical detail as my top of mind question is still --- do I need to get a new regulator?

That depends. If you want to experiment a little without spending a lot of money, get an old SP metal 2nd stage, specifically the balanced/adjustable or a 109 converted to balanced. Couv has a bunch of them and he's very reasonable.

My guess is that with the far improved heat transfer of the metal 2nd stage your problem will disappear, as long as you use good cold water technique. You could also try lowering the IP of your MK20 to around 125 PSI, but that might not be necessary.

If you do those things and still have a problem, it would make sense to get a fully sealed 1st stage. But there is no current 2nd stage that will have the freeze resistance of the balanced/adjustable, so you wouldn't be wasting your money on that regardless.