An update:
The sewellia were at it again last night. Unfortunately, so were the dithers.

That means the turn around time on spawning is as little as 12 days. Just a little shorter than it is with chenis and disparis.
This time, I saw what looked like a small puff of smoke. I'm sure that was the eggs and sperm. The eggs must be much smaller than chenis and a bit smaller than disparis that are about the size of a ( . ). I couldn't actually see them, because they were released in the bubbles in the strongest current flow. Lets hope the dithers missed a few.