Neutro CO2 Drop Checker

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CO2 Requirements

Better together


The Neutro Drop Checker is designed to indicate the amount of CO2 in your planted aquarium. In order to understand the CO2 level, a colour change occurs within the drop checker.

This drop checker is sold on its own and requires Neutro Bromo Blue solution to work and needs to be purchased separately. See the better together deal (on the right) and save money when purchasing this drop checker.


  1. Turn drop checker upside down and fill drop checker bulb section 3/4 full of bromo blue solution (sold separately). You may find using a pipette useful here.
  2. Turn drop checker right way up (without spilling contents) and place inside aquarium so that it is visible. In terms of location, aim for 2-3" off the bottom.
  3. Within 2 hours drop checker will display a reading according to your CO2 levels. Green is the ideal colour, yellow is too much CO2 and blue is too little (adjust CO2 output accordingly).

Key Point:

Remember your drop checker shows your CO2 levels 2 hours in the past (essentially a delayed reading). Any changes you make need to be done slowly. In the morning you want your drop checker to be showing a green colour so it's quite normal to have CO2 coming on about 2 hours before the lights come on. If you are new to CO2, then carefully monitor your fish in the morning to check they are OK. They should be fine but always check until you become familiar with CO2 levels and how your livestock are.

Final thought. The big question you have to ask yourself if you don't know your CO2 levels, how do you know if you have enough? 95% of all algae related problems are linked to insufficient CO2.

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by Jonathan B.
Seems to do the job. The liquid is very dark so it can be difficult to tell blue from green.

by Horace B.

by Stephen W.
What can I say. It's a good quality drop checker

by John S.
Neat, unobtrusive and works well.

by David Grubb
Nice and small, great price and does the job.

by Phillip Smith
nice and unobtrusive

Ask a question about this product
how often should the reagent be changed?


Depends which reagent you are using. Which one do you have?

How often do i change ae design 4 dkh solution with bromo blue in my ae drop checker?

Every 3-4 weeks is fine

How much Bromo Blue are you suppoed to use, bottle says 2-5 ml, 2ml fills it totally instead of half full as the description suggests? Cheers

Just as much as you want. 2ml is enough I would say :)

Does CO2 spread evenly in a tank? Am I right in saying that the best position for this drop checker is the opposite corner to the diffuser (I am talking about a small- say 60L- tank) not to get false readings? What would your recommendation be? Thanks

CO2 spreads where the water circulation occurs. Position your drop checker near the bottom of your tank close to the diffuser - the reason for this is quite often there will be little CO2 to the left/right of the drop checker and identifying the areas with the least CO2 is part of the secret to a planted aquarium.

If while fitting the checker into the aquarium, accidentally bromo blue mixes with water, is it harmful to fish or the plants for that matter- ?

Not particularly but I would definitely do a 30% water change as a minimum for the fish's sake

How do I clean the drop checker? Do I just rinse it with tap water or the 4dKH solution?


tap water - give it a good scrub. Tricky to clean inside so you might try a mild bleach solution over night then rinse under tap water for a few mins

Bought one of these yesterday, delivered today but it didn't have the sucker as shown in the pic. Is it meant to come with the sucker? If not, do you sell them as I can only see the clip type suckers on here which wouldn't work with this.

Pls email the office and we can send one out to you :)

looks like one of these awful plastic suckers that only last a few days before going hard and letting go? Do not want the chemical to escape into the aquarium.


They are rubber suction cups but they don't fall off. Certainly there's no chemicals that can escape into the water.

Do theas work with liquid easy carbo??



What is the height and width of this item?


about 5cm high and 3 wide (roughly)

If you use liquid CO2 is it essential you use this too with the Bromo Blue? Do you need anything else or is it just a case of using in this and checking the CO2 levels? If the levels are too high, do you just do a water change?


Drop check is only measure pressurised CO2 not liquid 

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