I have never seen a Combiplan tank in this country, so I cannot compare. Using half the chemistry would probably be a bonus using one shot processing, which is what I do. Speaking of chemistry amount. When you do get around to using your SP445, 465ml seems to be about just right. The film is covered at 450ml, just, with 480ml being the maximum before it starts coming out of the filler hole.
I tried 475ml yesterday and decided that it was just too much. After thinking about it, I then experimented and found 465ml allowed ample fiddle factor to ensure film is covered, yet still allows enough internal air space for the fluid to flow as you invert for agitation. there are at least a squillion ways to do agitation, my method with the SP445 is to do three inversions every 30 seconds. These inversions take about 8 seconds to do in total. I have extremely even development and am very satisfied at this stage of my journey with this quite portable film developing tank.
I originally purchased the tank with the idea to take it with me on trips, allowing me to develop at least some film to ensure things were working alright. Last year we were on the road for 3 months in extremely isolated areas of Australia. We had 4 weeks without anything available, communications wise, except satellite. Water quality isn't an issue as our camper has a ceramic micropore water filter for drinking use, better than the water quality at home, and Melbourne, reputedly has a pretty good water supply, or so they say. However, once I started using this little wonder of a tank, I find I'm itching to develop any film when I get home after a day out shooting. As I rarely shoot more than 4 sheets in a day, it is virtually perfect and has been a refreshing surprise.
Mick.
