Drop Checker with 4dKH Solution

The Drop Checker is an indispensable monitoring tool for any CO2-injected planted aquarium, providing a passive, continuous readout of dissolved CO2 concentration through a pH-sensitive colour indicator solution. The device hangs inside the aquarium, and aquarium water slowly diffuses into the sealed glass chamber where it contacts the 4°dKH reference solution — the colour shifts from blue (too little CO2) through green (optimal ~30 ppm) to yellow (excess CO2 danger zone) as carbonic acid levels change. The included 4dKH reference solution is pre-mixed to the correct alkalinity, ensuring accurate CO2 readings independent of the tank's own KH. The glass body is resistant to discolouration and easy to refill; simply top up with fresh 4dKH solution and a drop of pH indicator as needed. An essential tool for protecting fish and shrimp from CO2 overdose while maximising plant growth.