Can't make a decision !!

[diver 85]

It's possible your GF will need(use) less air than you---so a pair of 100's & 2 119s might 'match' up for the 2 of you nicely....----or 80s & 100s & on down the line.....

 

[japan-diver]

Dissimilar tanks is not a problem. Your air planning should be based on Rock Bottom calculations of air volume not pressure. Gas matching and rock bottom calcs are quite easy on dissimilar tanks and if you breath faster than your girlfriend than a slightly larger tank than her would be a good idea. Our regular dive group here shows up with everything from tiny 10l tanks to HP120's and we have not had a problem matching - you just have to plan in advance for the dissimilar volumes.

 

[MarcSnap]

To answer you question elan, I live near Montreal Quebec !!!

PerroneFord says

The scary thing now that you get this, is how many dives have you done with your GF or others where the dive wasn't turned with anywhere NEAR enough gas to get you both home?

Just started to dive last year and all my dives were with instructors or dive guide who called the dives not us... So now that we are buying tanks we are investigating more in depth the system PerroneFord.. I am sure that all the instructors that we went diving with,, took that in consideration during each dives..

 

[PerroneFord]

I am sure that all the instructors that we went diving with,, took that in consideration during each dives..

Based on my experiences with OW instructors and DMs, I'd bet real money they not only didn't take it into consideration, I'd bet they couldn't work a gas management problem without assistance.

I have NEVER seen an OW instructor that I know ever work up a gas management plan. Period. Even for deeper dives.