Thanks for the prompt reply. Specifically my problem and why I want separate SSIDs is a follows: I initially installed Deco M5s with both 2.4 and 5GHz enabled. Whenever I operate a particular appliance, the wifi feed to the box supplying subscription media services suffers interference and stops working. (Foxtel subscription services). Normal services are resumed when the offending device is turned off. The subscription service device talks both 2.4 and 5Ghz but obviously it connected to the 2.4Ghz service. I changed the Deco to run 5Ghz only and the problem goes away and everything works as it should and no interference occurs. EXCEPT that I have a robotic pool cleaner which wants/needs to talk to the cloud and it only talks 2.4Ghz so it no longer works. Thus I want separate SSIDs so I can connect devices to the band which works best - actually 3 SSIDs would be nice 2.4Ghz only, 5Ghz only and 2.4/5Ghz (as at present) for the default. (The current workaround is as suggested by others - start in 5GHz only connect the subscription box which then connects on 5GHz; then change the network so that both 2.4 and 5GHz are running and all seems OK and everything else works on whatever band they take a liking to - until something causes the M5s to power off.) Thanks.

  @RBAMilton 

 

There is another workaround, the one that I use at my house. Enable Guest Network with different SSID, run Main Network on 5GHz only, Guest Network on 2.4GHz only. Connect devices that can't handle 5GHz to Guest Network.