Probably are mate. All diesel's work on compression, that creates heat in order to burn the fuel, glow plugs creat that initial heat in order to get the compression ratio up to the correct temperature in order for diesel to burn... = low compression causes unburnt diesel that creates excessive black smoke.
Forget fuel treatments
Take out the glow plugs but leave them connected, leave them on a heat resistant surface. Turn on the ignition and see if the glow red hot within 30 seconds. If non of them do, then you have a relay issue. If only one , two or three glow, then they have failed, probably down to the coating damaged by the fuel treatment!
Clean and check The EGR valve/ Map sensor (do a search on MCSF errors)
Check your turbo hoses for leaks.
Once you have done all that, change the fuel filter and every couple of weeks take it for a long run at a constant speed on the motorway to avoid carbon build up and avoid short journey's where the engine isn't getting up to normal temperature then allowed to get cold before restarting
i.e. 5 miles to work, left for 8 hrs and return home.... If this is the typical case then get a petrol car... Diesel's prefer mile munching or you ask for trouble and expense otherwise