For future reference, I believe you misinterpreted the instructions for the inhibitor, and you drained the whole system when draining just a litre would have sufficed. And if you did intend to fully drain the system, that would have been better achieved by opening the radiator air vents.
Hindsight over, now what to do....
1. You have a Magneclean. Have you given that a full clean, not just an in-situ flush?
2. You say you may have flushed gunge from the F&E tank into the system. Have you inspected and cleaned the pump impellor? Many are rendered almost useless with debris blocking it. To do this you must isolate the pump (via its local valves), take the pump head off, and use a piece of soft wire (I find twin and earth cable earth wire is good for this) to prod out each 'slot' of the impellor. Are you competant to do this?
3. Once the pump is working properly it'll both move the trapped air to the bleed points more effectively and also move sediment (gunge) too, so a second flush of the Magneclean and a second pump inspection is advised in a week.
4. Beyond that a quick clean of the Magneclean 3 months later should suffice (more frequently if significant quantities of gunge are found).