Ugh, I'm going to have to do some conversions here. Anyone know off the top of their head what an increase of 170 CPM equates to in pCi/L? ;D

If you were using a standard tube type geiger counter like the GMC-200/300/300E/320 I could give you an idea only because I know what mine read when compared to the safety siren digital radon detector.

@Kingcobra, can you elaborate on the radon mitigation pump? Did you install yourself or have somebody do it for you? I have a passive system installed that was required when we built our home back in 98. However, I question whether or not my passive system does anything worth while.

Using a geiger counter on an air purifier with a graphing program you can verify how good your current mitigation system is working. If you test, please share your results. I would be very interested. Yours isn't outside is it?

Here is the pump I have:
http://www.menards.com/main/mobile/heating-cooling/ductwork/duct-boosters-accessories/radon-mitigation-fan-kit-4-with-air-pressure-indicator/p-1637326-c-6872.htm

No, mine is inside the house, basement with a 3 inch pipe that runs through my interior walls right up to roof of my home. Thanks for the tip on the device you are using!

BTW, pardon my ignorance, but why is a geiger counter PLUS airfilter combo recommended rather than just the geiger counter by itself?

I failed to answer your previous question.

My father-in-law and I installed it. I could have installed it myself, but my father-in-law has all the tools. I didn't want to go through the inside walls or look at the pipe going up the side of the house. I cheated and took it out of the house at ground level like a dryer vent. I know the experts say that is wrong because radon is heavy and will return if not vented at roof level. Even doing it the way I have, I got it from 18 pCi/ L down to 1.6 pCi/ L so I am happy.

If the geiger counter is put on the air purifier filter intake side the filter collects the radiation and allows better detection with the geiger counter. I use the same setup for my outside unit. If you use a filter with charcoal in it, even better. You know those radon test kits are small cans with charcoal in them.

Here is more good information on the topic:

https://www.netc.com/bb/viewtopic.php?f=7&t=460

This is also the method the EPA uses in their stations, though they have a much better standard design with a weatherproof housing and neat little circular, easily replaceable filters.

My understanding is that a filter is used because it traps radioactive particles and those are of interest because they are damaging if inhaled or ingested on food. I believe that the filter also will create somewhat of an average over time since there will be variation in the number of particles present at any one time.

The ambient radiation level (i.e. what you measure if you just use a Geiger counter with no filter) has an effect based on the level and length of time of the exposure, whereas the radioactive particles, I believe, can be worse because they continue to emit radiation in our bodies and can also cause burns to our lungs and digestive tract.

I don't know if the radon gas contains particulate or not.