I should update: It was almost certainly nutrient lock up I was running at pH7. Due to indicator solution being out by an order of magnitude. My uncalibrated meter was in fact almost spot on, I just checked it with proper buffered solution. The indicator drops do work fine as they are also calibrated to a calibrated meter! A golden amber colour should be 5 according to the drop chart, but it is fact 6, so if you know that it's ok. Everything is chugging along nicely now ;¬)
