Outdoor autos fan leaves losing colour !

I'm not new to growing, but always stuck to outdoors .

Here in the UK I've kept to Autos as more tolerate to our lower temperatures and unreliable seasons.

Currently growing in Coca mix with perlite (70/30) with a slight add of bat guano. Using all hesi fert products with correct NPK , with a small amount of liquid seaweed and sugar molasses.

Ph is 6.5 - 7 , with moisture levels slightly higher as was slightly keen on the water front.

Night time temperatures are not ideal at averaging at 50*-55* and daytime 70*-75* with minimal of 9 hours direct sunlight.

As pictures show , discolouration has occured from week 4 and seemed to have worsened. New growth seems healthy but after time starts to discolour.

My first thought was magnesium deficiency, which I have addressed this morning with a mix of Epsom salts direct to the soil (1tblsp / 4ltr) .

Would like any other review from fellow growers to see if I have diagnosed this correctly or if there are any other issues to sort

Thank you !