Okay...
PH run off is 6.8 same as whats been going in from the tap water and nute water. Everything seems good with that. I've transplanted all plants now into the bigger pots. The 3 I had already transplanted 3 days ago seem to be getting some green back into the yellow leaves
All the plants still look a litt worse for wear though. There is still extensive inward curling on the leaves and there is still a lot of yellow on the bottom fan leaves. I've got some better pictures with the HPS off so you might be able to recognise the problem?