I recently spent 6 months on Cozumel. I got most of my tanks(around 500) from one fill station where I hold an account. About a month ago I started noticing 3 ppm of CO and days later it went to 5 ppm. I alerted the filler but dove the tanks. It was the same the next day. I went by with my tanks and tester after the dive and showed them. They have a continuous monitor but I don't believe it was calibrated correctly. It turns out it was only on their nitrox. The next day they messaged me with gratitude and said they had found the problem and fixed it. I only read 0ppm on every tank after that. I will not name the blender. There are many on the island. I have tested positive amounts of CO from each of them at one time or another. One of the others was the one where I once tested in excess of 30ppm. I don't know how high it was because above 30ppm the cootwo that I use just flashes TOO HIGH. None of the other tanks on that boat read above 0ppm.
For reference, a smoker that isn't smoking at the time is constantly off gassing CO and will exhale about 17ppm continuously. The CO reading is important for what it may indicate is in the gas that you aren't testing for. It is a sign that indicates the health of the compressor and the condition at the time of pumping and may indicate combustion during the compressor operation which could indicate toxic byproducts.
For reference, a smoker that isn't smoking at the time is constantly off gassing CO and will exhale about 17ppm continuously. The CO reading is important for what it may indicate is in the gas that you aren't testing for. It is a sign that indicates the health of the compressor and the condition at the time of pumping and may indicate combustion during the compressor operation which could indicate toxic byproducts.