OK so having dosed the water over 24h ago now and turning up the heat to 28 degrees it seems to be having an effect. Some of the larger white spots have now fallen off my sword tail and still none of the other fish have contracted it yet.
I also did a 20% water change of both tanks this morning as I’ve lost 3 guppies in the new tank and a 4th looks on its way out. I figured its nitrogen cycle wasn’t upto speed yet the tank has been setup 10 days and only had fish in it like 3 days so to help keep the nitrates, nitrites and amonia low I did a water change. It seems to have worked and the remaining fish seem to be happy and active so thats good.
My only concern now is the 2 red tailed sharks one of them is loosing its colouring which I read is due to stress and between the new tank and being bullied a little by the other one (kept its markings strongly). I really hope that I can sort out the whitespot in the small tank pretty fast so I can get the big fish moved over and one of the red tails moved back to the small tank to keep them separate.