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Established 1989
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Code: 2413800
  • £16.99
Item in Stock   |   Usually dispatched within 24 hours

Permanent test to determine the acid/carbon dioxide content in freshwater aquariums

  • Simple and reliable monitoring of the aquarium water values. Permanent direct measurement of the pH value and carbon dioxide content in freshwater aquariums
  • Permanent test for fertiliser control: place reagent in the permanent test device and attach to the aquarium pane, using suction cups. Compare reagent colour with colour scale sticker and read off value
  • Indication of pH value (6.4 – 7.8) and CO2 content
  • You will find detailed information and troubleshooting tips about water analysis on the JBL website in Essentials/Aquarium
  • Package contents: 1 CO2-pH permanent test, display vessel with suction cup, 1 reagent (+ 1x refill) and colour scale sticker. Reagent refill and indicators separately available

This permanent indication test uses colouration to show the aquarist the pH value and the CO2 content of the aquarium water at any time.
You can read off whether the pH value is within the optimal range and whether the plants have sufficient CO2 as their main nutrient available during the day 24/7.

How exactly does the test work?
The CO2 dissolved in the aquarium water diffuses in the container of the permanent test, passes into the air column containing the indicator liquid and then dissolves in the liquid. This creates a pH value, which results in the discolouration of the indicator liquid. The colour displayed corresponds to a certain pH-value and, depending on the carbonate hardness of the water, you can read off whether the resulting CO2 content is too high, too low, or optimal.
If another pH-lowering or increasing substance (e.g. pH-Minus) apart from CO2 is added to the aquarium water, it cannot diffuse through the air column in the permanent test and thus does NOT affect the indicator liquid. In this case the pH value displayed would not be correct. It only shows correct values, when there are NO other pH-influencing substances in the water besides CO2.

How long does it take until the test displays correctly?
Due to its design the test is somewhat sluggish, because the CO2 gas needs to first "migrate" through the air column in the test vessel, then into the indicator liquid and can only then be displayed. It can therefore take up to one hour until the test shows the current CO2 content of the aquarium water for the first time.

Recommended CO2 content:
Freshwater aquarium (community aquarium): 15-35 mg/l;
Lake Malawi-Tanganyika aquarium: 4-10 mg/l;
Plant aquarium with few fish (aquascaping): 20-35 mg/l

Contact us with any questions you have about this product

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Next Day Shipping Upgrade - Cut off is at 4:00 pm

Orders after that time will be processed the next working day


Please Note: We only deliver ponds and pond plants on our own delivery vehicles!

The blue highlighted area on the map below is where we deliver on our own vehicle! Unfortunately, if you are not in one of these postcode zones we are unable to deliver certain items such as plants, small glass items and selective other products.



We offer a few different delivery options depending on the size and value of your order.

Orders over £50 qualify for free mainland UK (excludes Northern Ireland) delivery which will arrive within 3-5 working days of the order being processed.


Residents of Northern Ireland, please provide your EORI or XI Number.

If you do not have one, please follow the information at


Orders Below £50 in Mainland UK will be charged a standard delivery fee of £5.99.

Additional Shipping Charges

For any orders that do not include Aquariums, the below is charged:

Next Working Day Parcel Delivery to Mainland UK - £7.99 OR £2.99 if the order is over £50

Standard Parcel Delivery to Northern Ireland £8.99

Standard Parcel Delivery to Scottish Highlands & Islands £9.99

Standard Parcel Delivery to Jersey & Guernsey £12.99


For all Aquarium deliveries (Excluding biOrbs & Smaller Aquariums), the below is charged:

Next Working Day Pallet Delivery - £20

2 Hour Booking Slot Pallet Delivery - £20

Pallet Delivery to Northern Ireland - £45

Pallet Delivery to Isle of Wight (PO36 and Above) and Scottish Highlands (AB, PH, IV1-36, IV, KW1-14, KY, PA21-41) - £45

Pallet Delivery to the Scottish Isles (KA27-28, PA60-90, ZE, JE, GY, IM, IV40-56, KW15-17, PH42-44, PA20, PA42-49) - £120

Pallet Delivery to Outer Hebrides (HS) - £140