Good looking grow, Graham.
Most sources reference pH 7.0 for a soil grow and 6.0 ish for coco. pH of 8.0 is TOO high and is preventing vital nutrients from being available to your plants. I am assuming that pH is your problem and not lack of N fertilizer or other cause.
If a pH problem, that ry mixing up 5 gallons of water at pH 6.0 or so using GH pH Down (a mild phosphoric acid solution - ~$20/quart, should last all grow). Then hand water your plants with it. Next waterings, pH the water to recommended soil or coco pH. This should drop the pH to where it should be. You can also pH test the run off to check it. Yes, this is an inexpensive, easy fix.
Using the sprinklers for direct watering is probably not advisable.
I had a bad pH meter a year or two ago and the plants were not growing as well as I expected - pH too high. Once I identified the problem with a new $15 pen type meter, they recovered nicely with lots of frosty buds.