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The CO2 Drop Checker (often called a glass trumpet or bell) is the most reliable way to monitor the gas levels in your aquarium. It acts as a permanent visual gauge so you can see at a glance if your plants have enough fuel or if your fish are in danger.
Here is the essential guide to using it, with all the technical clutter removed.
The liquid inside the glass changes color based on the amount of gas in the water. Since there is a slight delay in the reaction, always wait about two hours after adjusting your gas before trusting the color.
Blue: Not enough CO2. Your plants might grow slowly or algae might start to appear.
Green: The "Sweet Spot." This is the target for a healthy, balanced planted tank.
Yellow: Too much CO2. This can be dangerous for fish and shrimp. Turn the gas down immediately.
Fill the Bulb: Add the indicator solution into the glass piece until the rounded bulb is about half full.
Mounting: Use the suction cup to stick it to the inside of your tank.
Positioning: Place it on the opposite side of the tank from where your bubbles come out. This ensures you are measuring the gas that has actually dissolved into the water, rather than just catching bubbles as they float past.
The Air Gap: Ensure there is a small pocket of air between the aquarium water and the blue liquid. The gas travels through this air pocket to change the color of the liquid.
Monthly Refresh: Change the liquid inside the drop checker every 4 to 6 weeks. Over time, the solution loses its accuracy and might stay "stuck" on one color.
Cleaning: If algae grows on the glass, just wipe it off with a soft sponge during your regular water change.
Avoid Contamination: When doing water changes, try not to let the aquarium water splash inside the glass opening, as it will ruin the reading.
