How It Works
Drop checker has a chamber of 4 dKH solution plus pH indicator (bromothymol blue). Tank CO2 dissolves into chamber slowly, changing color.
Blue = CO2 below 15 ppm. Green = 25-35 ppm (ideal). Yellow = over 40 ppm (dangerous for fish).
4dKH Solution Preparation
Mix 1L distilled water + 0.12g baking soda (sodium bicarbonate). pH should be 7.5-7.8.
Why not tank water? Different KH makes readings wrong. 4 dKH is the standard.
Placement
Place drop checker in the tank near middle, not near CO2 diffuser. Readings are 1-2 hours behind actual CO2 level.
CO2 should reach green by the time lights come on, not after.
Calibration Check
Change 4 dKH solution every 2-3 weeks. Old solution gives false readings.
Test before refilling — check pH of old solution. If way off 7.5, indicator is contaminated.