Typically I dip as clean a sample as I can with a spoon off the top onto a white plate and drip iodine on the side and watch the junction between the two for any black.
Today after batch sparging my first runnings I retested and it showed complete conversion where as my last test of the wort from the top of the cooler tun still showed a slight reaction.
My recipe today was:
2 lbs 15.7 oz Pale Ale Malt 2-Row (Briess) (3.5 SRM) Grain 1 55.1 %
1 lbs 6.1 oz Munich 10L (Briess) (10.0 SRM) Grain 2 25.6 %
9.5 oz Caramel Malt - 40L (Briess) (40.0 SRM) Grain 3 11.0 %
4.8 oz Caramel Malt - 60L (Briess) (60.0 SRM) Grain 4 5.5 %
2.4 oz Extra Special (Briess) (130.0 SRM)
I crush pretty course with a few kernels only split in half with a good number of large hull.
I use a traceable lollipop thermometer but I double check with a big daddy dial.
Doughed in today to 149.5 with a target of 150. It held 145.9 for an hour and dropped to 148.5 by hour 2.
Batch sparged and collected 4.15 gallons (doing a 2.5 gallon half batch 90 minute boil)
and my preboil gravity was 1.035 @ about 75% efficiency all according to Beersmith.
I think your right, flawed iodine test. I need a new test