Midges hatch in still water starting in the spring and can continue hatching almost daily into the fall. The low light of morning or evening is prime time but on a cloudy day midges can hatch throughout the day. Trout will cruise just under the surface and pick off the pupas or adults, sometimes with a head-tail rise but usually there is just a boil on the surface. Fishing to trout midging in still water is challenging. Rising trout in flowing water usually stay in one spot and an accurate delivery is not difficult but trout that are rising in still water are cruising and if you cannot see the fish it is usually a guessing game where to make your cast.
I used to fish an adult pattern with a pupa dropper and would cast and just let the patterns sit or hand twist them and hope the cruising trout that rose would see them. This technique worked but most of the fish I hooked were on the pupa, so I decided to try using two pupas fished with a standard chironomid hand twist retrieve. Fishing two pupas was effective and increased the odds of a fish seeing one of the flies. This was effective but my hook up rate increased significantly when I started using a flash back pupa for the first fly with a plain pupa trailer. I hook fish on both patterns, but am convinced that because of the flash on the first fly more fish see the flies.
If I cannot see the fish and am just casting to rise forms I fish 4x Fluoroflex Plus to the flash back pattern and tie the dropper off the bend to around 24 inches of 5x Fluoroflex Plus. This relatively heavy tippet set up may result in fewer takes than 5x followed by 6x but will cut down on break offs when a large, cruising trout unexpectedly takes your fly. You are casting to where you think the fish may be swimming but basically you are blind fishing and it is easy to reflexively set a little toohard if you are not 100 % ready. If I can see the cruising fish it is easier to time the hook set and I use 5x to the first fly and 6x to the dropper.
To increase the odds that a cruising trout will see the flies it is important that you fire the cast in quickly after you see a rise or boil. I usually fish out of a float tube when hunting midging trout and just slowly kick around looking for rise forms. I strip out as much line as I can pick off the water with one back cast and just let the pupas trail behind me. If I see a feeding trout I make a back cast with the trailing line and fire it to where I think the fish is swimming. If a rise is close I will strip in some line before making the back cast. I then start a slow hand twist retrieve and tell myself to set the hook gently.