Review on Fluval A7551 CO2 Indicator Kit by Lalaine Fernandez

Product works and is good for a quick reference, especially for beginners. I can easily see what color it is from across the room or even from another room. If I look and see that it's light green I can make adjustments before the fish show any signs. Or, if it's blue, turn it on. It should not be used to get an exact value, there is no indication of what the actual PPM is. If you're looking for actual CO2 readings, make sure you have pH and KH liquid tests available. Use the online calculator to determine CO2 based on these two readings. The only complaint is that it takes time to adjust to current levels. Expected based on how it works. Also, they supply a very small bottle of liquid. They say it's only good for a couple of weeks before you need to replace it, and then you have to spend more on it.