CO2 levels that are too low won't fuel plant growth, and levels that are too high overnight can stress fish, but neither extreme is visible without a way to actually see dissolved CO2 in real time. The Dymax Crystal CO2 Indicator (drop checker) and CO2 Indicator Solution give you a constant, at-a-glance color reference for what's happening in the water.
Why a Drop Checker Beats Guessing
Bubble rate tells you how much gas you're injecting, not how much CO2 is actually dissolved in the water — factors like flow, tank size, and plant mass all affect the real concentration. A drop checker uses a color-changing indicator solution sealed against a small air pocket to show the actual dissolved CO2 level continuously, not just a snapshot.
How the System Works
- Crystal CO2 Indicator — a small glass chamber that suction-mounts inside the tank, holding a reservoir of indicator solution against an air gap that equalizes with tank CO2 levels.
- CO2 Indicator Solution — the color-changing fluid inside the checker; it shifts from blue (too low) through green (ideal range) to yellow (too high) as dissolved CO2 changes.
How to Read and Maintain It
- Aim for green as your target color — blue means more CO2 is needed, yellow means you're overdosing and should scale back.
- Give it time to respond — a drop checker lags behind real-time changes by roughly an hour, so read it consistently rather than right after adjusting your injection rate.
- Refresh the solution periodically as it evaporates or degrades with use, since exhausted solution stops giving an accurate readout.
The Dymax Crystal CO2 Indicator and Indicator Solution are available at Marine Concept Supply — order online or pick up at our shop in Wheeling, IL. Shop the CO2 Indicator or Indicator Solution, and browse more CO2 & planted tank supplies.
