It happened again ... I did another 25% WC today (no pruning, touched the substrate ever so slightly - moved a plant a little) and 30 minutes letter I have the cloudy / foggy water again. No particles, just foggy.
This also happened the last time (Wednesday) I did a WC - we thought it was because I had did a major plant trim the day before. This time I didn't. Last time it cleared up by itself within about 5 or 6 hours.