Thanks for your help. Last night I took 25% of the tank water out using a gravel vac, I then took out all the plants etc. and scrubbed all sides of the glass to get the 'white stuff' off (I ran my finger over it and it was slimey?). I then syphoned out another 25% of the water and re-filled it back up with new water. I am hoping this will improve it a bit!
They are definitely not bubbles, they move with the water current. It is stuck to the glass and is about 1mm in length but there are millions of them. I looked a hydra but it definitely isn't that either! I have looked everywhere but can't find any pictures similar to tell me what it might be!
Do you think it's worth trying flourish excel to see if it helps?