I think anything below 100' can benefit from some He in the mix. A dive towards 150' should be a Trimix dive for sure.
Co2 buildup could be very possible factoring in current, age, Diver's location (NY - likely not dove recently). This is highly speculative - I know. It also points the ABSOLUTE need for a SMB and other signal equipment (mirror, streamer, whistle, etc.) while diving offshore in a dynamic environment like SE Florida.
** Disclaimer - I only felt the need to respond since the majority of my dives have been in this part of the world **