Update!
Went to check on things 2 days ago, and decided to swap the straight coupling that connects the PVC to the hose for an isolation valve. The reason for this, is to control the pressure into the manifold, so I can turn the isolation valve until I have reduced the pressure to a "drip" from the drip rings. I want to feed the plants slowly over a longer period of time, rather than saturate them in 1 minute.
I fitted it, turned the pump on, then noticed that none of the rings where working correctly. Some holes where squirting out, some where slowly dripping and some weren't releasing anything at all.
I wasn't surprised to be honest, as I've been warned about this by members on the forum. Obviously fine particles of coco must be entering the system and blocking the holes I made. (The holes were only pierced, so not very big at all)
Also I noticed that, in 2 areas of the table, the nutes weren't draining properly into the guttering. I watched, and discovered that at the very edge of the corrigated sheet, the nutes were building up and running underneath the plastic and soaking the wooden frame, then dripping onto the floor.