That's great. Thanks for posting the progress. It never even crossed my mind you may have midge larvae flourishing in your tank
Clown loaches, although advertised that they like flow, actually do not like extreme flow and I've never seen mine playing in the flow of an outlet, although I've seen fish coming from calm waters that get excited when they see flow. I initially kept mine in a tank that turned over 20X the water volume an hour, extreme I know...I noticed they were hiding a lot. I had a powerhead additional to the filtration, around 740G/H. I turned that off and voila....clown loaches out all the time....
I think its important having an oxygenated and over-filtered tank for them but a powerhead is not needed...
Generally, I recommend 10 times the water volume turn over for clown loaches....in filtration and not powerheads(going by the stated manufacturer's rate as actual flow is lower) They'd do really well in that and if the tank is properly stocked and water changed to min 50% once weekly, I'd be suprised if you ever have any issues with your clown loaches, disease and health wise.
Please post more pictures of the clowns. Do you have before and after? It would be great to see the progress from skinny to fat loaches