CDS @ only a 1000 ppm

Hi, 
Sorry if this question has been asked before but I've tried to make CDS via the Andreas Kalcker method but can only get my end product to 1000 ppm, I'm using Sodium Chlorite 80% diluted in distilled water to 22.4% and Hydrochloric Acid 36% diluted with distilled water to 4%, I do the shot glass in an air tight jar 12/24 hour process and all seems to be going to plan, but then when I add 1ml of end product to 9ml of distilled water expecting it to be at 3000 ppm but its only indicating 1000 ppm on the test strip, I've done the process a few times now and each time is the same end result, can anyone shed any idea on what could I possibly be doing wrong? many thanks.

Is your container as airtight as possible? Is the gas escaping? Can you smell the chlorine dioxide in the area that you leave the container? You can use plastic wrap to seal it tighter.
What test strips are you using. The LaMotte #3002 Test Strips seem to be the only ones that are reliable.

My container is airtight, if I tip it upside down nothing escapes/leaks also no smell whatsoever, with regard to the test strips I'm using there doesnt seam to be a name on them, just the name of the company I purchased them from which is DCS water treament (in UK) they measure up to 500ppm, my guess is they remove the original label and stick their own on it, I have recently found strips that test up to 3000ppm but as of yet have not purchased them.

People have tried many brands and only LaMotte seems to give consistent correct readings. Try get some of those #3002 LaMotte test strips to see if it makes a difference.
Remember to cut them in half to get twice as many!