If you are just looking for classes to challenge yourself or add interest to your diving, consider an Intro to Tech, or GUE Fundamentals class. You can certainly do Fundies in a single tank, and depending on instructor, you may be allowed to take other agencies' Intro to Techs that way, too. Such classes will emphasize really fine-tuned personal diving skills, as well as introducing some concepts like gas management and a more nuanced approach to ascent strategies and decompression. Best of all, the things you learn in such a class would be immediately applicable and useful to any recreational, single-tank diving you do.
You have a GUE instructor not too far from you -- Steve Blanchard is in Ottawa, and I know he does a lot of diving in the St. Lawrence and in the lake.
You have a GUE instructor not too far from you -- Steve Blanchard is in Ottawa, and I know he does a lot of diving in the St. Lawrence and in the lake.