NT LABS Marine Lab Carbonate Hardness Test

What is KH?

KH, or carbonate hardness, describes the pH buffering capability of water. Water with the correct KH will resist changes to the pH, ensuring a stable environment for your aquarium’s inhabitants. KH measures the concentration of carbonates and bicarbonates dissolved in the water which provide the pH-stabilising effect. In a reef aquarium, these are also an essential component for reef-building corals and other invertebrates with calcium-based exoskeletons.

Why test for KH?

As marine water ages, acidic processes in the aquarium consume the KH causing it to decrease. Furthermore, many marine invertebrates assimilate carbonates removing them from the water column. If the KH becomes too low, the pH of the water is at risk of significant fluctuations. It is these changes that cause stress to fish and make them more susceptible to disease. The KH should be tested frequently to ensure that it remains at the correct level to provide a stable environment for your aquarium’s inhabitants.

What is the correct level of KH?

In natural seawater, the dissolved carbonate hardness is normally 7 dKH (or °KH), but you may wish to maintain a level between 7 and 14 dKH depending on your method of running the aquarium.

What to do if the KH level is wrong?

If your KH is low in your aquarium, use Marine Buffer Powder to safely increase the KH up to the desired level. Monitor the KH frequently to determine how quickly the KH decreases over the period of a week and adjust to frequency of water changes or addition of buffer to maintain a stable KH. If the KH in your aquarium is high, a water change with a good quality salt will help reduce the KH, but changes to KH should be carried out slowly to avoid stressing the inhabitants.

How to test for KH?

• Add 5 ml of water to be tested into the test tube provided. The middle mark on the test tube indicates 5 ml
• Add 1 drop of the KH reagent to the test tube and mix – the colour of the sample should turn blue.
• Continue to add the KH reagent, one drop at a time with mixing until the colour of the sample changes from blue to yellow, counting each drop.
• When the colour changes to yellow, stop the test.
• Each drop of KH reagent used, including the first drop, indicates 1 dKH. For example, if the sample turns yellow after 7 drops, the KH is 7dKH. To convert from dKH to mg/l (as CaCO3), multiply the dKH by 17.8.

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Next Day Shipping cut off is at Noon/12:00pm

Orders after that time will be processed the next working day

Please Note: Certain ponds, aquariums, all pond plants, and all livestock are excluded from free delivery.

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.

Certain orders over £50 qualify for free mainland UK (excludes Northern Ireland, Pond Plants, and livestock) delivery which will arrive within 3-5 working days of the order being processed.

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

Pond Plant and Tropical/Marine/Pond Livestock will be charged a delivery fee of £19.99.

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 (excludes Northern Ireland)

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, Medium - Extra Large Terrarium/Vivarium/Paludarium deliveries (Excluding biOrbs & Smaller Aquariums), the below is charged:

You must be present for delivery and please check your item before signing for delivery.

A payment link will be sent to you if redelivery is required.

Next Working Day Pallet Delivery - £20

2 Hour Booking Slot Pallet Delivery - £20

Pallet Delivery to Northern Ireland - £45

Saturday and OptiClear 90 & 120 Delivery - £60

Pallet Delivery to Isle of Wight (PO30 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

Pond's over 1000 litres will be a curb side pallet delivery.

Aquariums over 125 litre will be a curb side pallet delivery.

The couriers we use are Royal Mail, DX, APC, and UPN.

Standard Delivery

Northern Ireland Standard Delivery

Next Day Delivery

Cut off is Noon/12:00pm

Saturday Delivery

Cut off is Noon/12:00pm

Livestock Delivery

Cut off is Noon/12:00pm

Plant Delivery

Cut off is Noon/12:00pm

Standard Curb Side Pallet Delivery

Cut off is Noon/12:00pm

Next Day Curb Side Pallet Delivery

Cut off is Noon/12:00pm

Saturday Curb Side Pallet Delivery

Cut off is Noon/12:00pm

Northern Ireland Curb Side Pallet Delivery