We’re doing to Carbonate Hardness Test to check the KH level of the tank behind me. The reason you check your KH is that the KH controls your pH level in your aquarium. If you ever come back from a holiday and find that all your fish have died, it is likely due to a drop in pH level. This drop in pH level is caused by the lack of carbonate hardness in the water.

KH Testing

I’ve got one sample we have from the tank behind me. If you put one drop of the liquid in the vial with 5ml of water and shake, you can see the liquid is yellow or clear tap colour. Ideally, what we want to happen is to go blue and stay blue for at least three or four drops. When the water test comes up yellow or clear, the carbon hardness is on zero, which means the pH is very unstable.

To begin with, I’ve put the carbon hardness increaser in the tank. Now, let’s check whether the solution goes blue instead of staying yellow. To do this, put five ml of water into the vial, then add one drop. Initially, the solution was yellow, but upon adding the first drop, it should turn blue, indicating that the carbonate hardness has improved and the pH is more stable. You can add more drops and continue shaking until the top of the water starts to change yellow, usually after six or seven drops. If the seventh drop turns the liquid from blue to yellow, then that is equivalent to seven German degrees, indicating a very stable pH. For tropical tanks, four drops before turning blue is optimal, while this aquarium, with its high KH, is perfect for fish like African Cichlids.


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