Helicon is the way to go.
Flow MUST be off. Helicon will align the photos properly, but everything needs to be in exactly the same place inside the tank or it will look all fuzzy.
F/9 is perfect, you could even go to F/11. Just make sure you overlap your focus a little. SUPER TINY adjustments all along the way will give you the best results.
Also, just for reference, i use light room to batch process the photos to get them all white balanced. Then i export them as a .TIF files (for whatever reason, this gave Gary the best results, and was the same for me too).
I process the .TIF files in Helicon, and save the final result in .jpg.
If needed, you can then crop and sharpen the image further in PS.
Its quit a process, but well worth the time. Once you get the process down, start to finish wont take more than ten minutes.
Good luck, if you have any questions, feel free to ask.