Sure is and its giving you a clear message too.
If your drop checker is staying blue, there is almost zero CO2 in your water. But here's the thing...
Drop checkers don't actually monitor CO2, they monitor pH. When you add CO2 (an acidic gas) into your tank, it reduces the pH. When your drop checker is showing blue, it's telling you the pH is around 8 (far too high for plants). As you inject CO2 your drop checker will change colour (assuming you're injecting enough CO2). The solution will begin to look a bit more green. When it hits a nice shade of green it means your pH is about 6.8 and your CO2 levels are 30ppm (parts per million). Green is the ideal colour to aim for and what you need to strive for.
But all too often hobbyists don't inject ANYWHERE ENOUGH CO2. In a 100L tank, you need to start with 1 bubble per second for 8 hours a day.
Any changes you make to your CO2 flow rate needs to be done slowly. Remember your drop checker operates in the past - it's not like a test kit in the respect that you take a sample of water and do a reading. There's a delay of about 2 hours - this is how long it takes for your drop checker to change colour. So if you tweak your CO2 levels now, wait 2 hours, then see what colour it has changed to.
Always make small gradual changes to CO2 flow rate, otherwise you could overdose your fish with CO2 and see them gasping at the surface of your tank.
Make sense? Any questions?
