Help w/finding a reliable co2 monitor/controller.

Hey riu! Just hoping I could get some advice as to what co2 controller/monitor to buy.
What Im looking for is a unit that will constantly measure co2 levels and automatically kick on/off to maintain a designated level of ppm. I don't really want to set it on a timed cycle.
Many advice is welcome, I've looked for some but honestly haven't the slightest clue of what is reliable and effecient.

90 plus views and no response. I know RIU is better than this. If anyone has input please post it.

I'm looking for the same, but only for about 24 sq.ft of space. Anyone got anything?

I personally use one of these: http://www.amazon.com/C-A-P-CAP-PPM-3-CO2-Controller/dp/B000QFMZES

I bought it at a local store half price because they were going to s top carry CAP products. My original intention was to spend a little more money and get something from titan controls: http://www.titancontrols.net/products/co2-devices.aspx

That being said, I figured if i could get a year out of the CAP controller, I would be happy with what i spent, and its still working after about that long. There is a little bugginess with it, a well known issue where it will just get stuck at a certain level and stop working randomly. I resolved it by putting it on a timer that turns it off for 1 minute every four hours to reset the thing, and that resolved all my issues. Reliably controls my water cooled CO2 generator setup. This controller comes under multiple brands, i believe CAP rebranded a device that was originally made by GE. If you are looking for the lowest price, you can probably find this one cheapest under $300 or so. If I ever had to replace it, I imagine I would pony up the money and get a sentinel or titan, but expect to be into one of those at least $400-500. Id definitely reccommend one that has a digital read out for CO2 levels. I don't trust the ones that just have a light that comes on when its in the proper range.

Here's another option:

http://www.co2meter.com/collections/fixed-wall-mount/products/co2-level-controller

Since I work for the company, you should take it with a grain of salt, but they are made in the USA, great support via toll free number and for an extra $79 you can get a USB cable to fine-tune CO2 levels.