Later in the evening I heard splashing. Have noticed this a few days in a row now- some time after the lights go out, I hear momentary dripping or splashing from the tank. I thought I had a leak, but no sign of that. This day it occurred several times in a row- finally I sat in front of the tank and waited for it. One of the striped kuhli loaches was swimming up the filter outflow! I got a view from above the second time it happened in front of me, and he darted up far enough to get bumped back by the turning wheel.
Now I don't know if the kuhli was trying to escape because of poor water? or responding to weather changes- we did have a large drop in temperature last night, and I've heard these loaches can get very active with changes in air pressure, including escape attempts! It was late, I was tired, I did what I could think of to prevent a fish getting out in the night.
But I sat there another hour and it didn't occur again- maybe the netting baffles the outflow of water enough that it doesn't attract the fish anymore? I was relieved that I didn't find any loaches stuck in the netting in the morning or missing from the tank, but I need to find another solution to this. Maybe I'll lift off the filter box on maintenance day so I can fit the netting on there more tidy.