A quick update on the ranchu. Today they received a full water change and temperature increase to a little under 18.5 degrees C. The ranchu became very active, on returning to the water, with a lot of breeding like behavior. What I had believed to be 3 males have been almost certainly confirmed, as they were all chasing and butting female ranchu, as well as posturing and chasing each other. Pectoral breeding tubercles also became very prominent on two of the ranchu.
I added spawning material and was out for the rest of the day. Nothing has come of it yet, although I could make out some gentle chasing occurring a short time ago in the dark and wouldn't be at all surprised to see lots of action one morning this week.
Based on this mornings activity, my 4 favorite ranchu appear to be split evenly 50/50 male/female. This is exciting as I hope it will give me a couple of different pairing opportunities which will be of great value in assessing best pairings for the future.