CO2 Drop Checker & pH Pen
AQUARIO_GENERIC_DROP_CHECKER_CO2
A CO2 drop checker is a glass indicator that monitors carbon dioxide levels in a planted aquarium by changing color based on the pH of a 4 dKH reference solution:...
Or build it into a bundle — save up to 6% ↓What it is, and who it is for.
A CO2 drop checker is a glass indicator that monitors carbon dioxide levels in a planted aquarium by changing color based on the pH of a 4 dKH reference solution: green indicates optimal CO2, yellow means too much, and blue means too little. It gives a reliable visual reading roughly 1-2 hours after placement. The representative unit shown is the UNS Drop Checker, available in suction-cup (SD) and rimless hang-on (HD) styles and supplied with indicator solution; a pH pen complements it for precise readings.
Build around the CO2 Drop Checker & pH Pen.
It's already in your system below. Add the flow, filtration and dosing around it and the discount starts working — tiers climb as the build grows, and the reef meter fills with it.
Pick the right one, not the biggest one
The honest line-up from test kits. Most buyers reading this page should buy the middle column.
TDS Pen Water Tester
CO2 Drop Checker & pH Pen
JBL ProAquaTest Freshwater Test SetAsked before checkout
The questions our support inbox actually gets.
Does it ship quickly?+
Orders placed before 2 PM ET on a business day leave the same day. Tracking is emailed the moment the label prints.
What if it's the wrong fit for my tank?+
Return it. 30 days, no restocking fee, refund to the original payment method. Better: tell us your tank first and we'll spec the system for free — half of all returns are sizing problems.
Who handles the warranty?+
We do. Everything carries the manufacturer's warranty and we run the claim for you — one email to us instead of a ticket queue.
How does the bundle discount work?+
Add items in the bundle builder: 2+ items saves 5%, 3+ saves 8%, 4+ saves 12%, and 5+ saves 15% off the whole system, applied at checkout.