I missed the bit somewhere where he over filled.The statement to ignore that air gap is certainly the recommended procedure to use any syringe, but it might confuse the OP here since he is presumably forced to measure from the air/water interface both at the start and finish of the titration (which is OK) since he overfilled the syringe past the 0 mL line and pulled the air/water line up to the 0 mL line.
For the OP, here's how to properly read a syringe:
Reef Chemistry Question of the Day #161 Using a Syringe
Reef Chemistry Question of the Day #160 I have just drawn tank water into a syringe with a tip (shown below, including a blowup of the barrel). The blue coloration shows where the fluid is. When I started to draw fluid in, the tip and syringe were empty and the plunger was all the way in...www.reef2reef.com