PH Probe

I didn't know they did them in NZ - that's fantastic - it's the most definitive test for reflux. I know of them being done in adults (but don't think it's done under the public health system in NZ).

Cut and pasted from a few websites:
A 24-hour pH probe is a fairly accurate test that shows any increased levels of stomach acid in the esophagus. A long, thin tube that is attached to a machine is placed in your child's esophagus (via her nose or mouth) by a doctor or nurse. The end of the tube reads the acid level and records it on the machine after each feeding. After 24 hours the doctor will determine if the amount of acid in the esophagus is too high indicating GER. This test can be performed at home, however, some doctors prefer to hospitalize the infant during the test so a nurse can replace the probe immediately if it accidentally comes out.

pH Probe- A pH probe is used to quantify gastroesophageal reflux. A small tube is placed through the baby’s nose and down into the esophagus. A small sensor on the end of the probe detects acid when the child refluxes. The parents can push a button for markers when the baby is having symptoms so the doctor can see if they correlate with reflux. The pH probe lasts for 18-24 hours.

Hope you get some answers and treatments soon. Sounds like you have been seen by paeds - fantastic.