API GH/KH Hardness Test Kit

• Two parameters, one kit – GH and KH each get their own dedicated reagent bottle and test tube.
• Titration method, not a fixed test count – you count drops until the colour changes, so soft water uses fewer drops per test than hard water. See the note below.
• Results in degrees – read as °dGH and °dKH, with a conversion note in the instructions for converting to ppm.
• Freshwater and saltwater – the same reagents work for both.

KH test: fill a test tube with a 5 mL water sample, add the KH solution one drop at a time, capping and inverting after each drop, and counting as you go. The test is complete when the sample changes from blue to yellow.

GH test: fill a test tube with a 5 mL water sample, add the GH solution one drop at a time, capping and inverting after each drop, and counting as you go. The test is complete when the sample changes from orange to green.

The number of drops needed is the reading – each drop typically represents one degree of hardness, per the conversion chart printed in the instructions.

Unlike API's colour-match kits, this is a titration test: you add reagent drop by drop until the colour flips, and the drop count itself is the reading. That means a soft-water tank (fewer drops needed) gets more tests out of the same bottle than a very hard-water tank (more drops needed per test). API does not publish a fixed test count for this reason, and quoting one would misrepresent how the kit works – so we haven't.

Included:

• KH test reagent bottle
• GH test reagent bottle
• Two glass test tubes with caps
• Instruction sheet with degree-to-ppm conversion

Not included:

• A printed colour chart – this kit reads by drop count and colour change, not a comparison card
• Anything to raise or lower hardness – test only

Suitable for:

• Freshwater and saltwater aquariums where GH and KH need tracking – planted tanks, shrimp tanks, African cichlids and reef systems all care about this pair
• Diagnosing pH instability – a low KH reading usually explains a pH that won't hold steady

Not suitable for:

• Correcting hardness – this kit measures only
• Colour-blind users without assistance – the endpoint is a colour change, so a second person or a well-lit comparison helps

• Keep out of reach of children.
• Avoid eye and skin contact with the reagents; rinse well with water if contact occurs.
• Shake reagent bottles vigorously before use, and keep the cap closed tight while shaking.
• Rinse test tubes immediately after each test to stop reagent residue staining the glass.

• API Freshwater pH Test Kit – KH is what keeps a pH reading stable between tests, so the two go together.
• API Deluxe pH Test Kit with Liquid Adjusters – check KH before repeatedly dosing a pH adjuster into a tank that keeps drifting back.
• API Freshwater Master Multi Test Kit 5 in 1 – rounds out your routine testing with ammonia, nitrite and nitrate.

This is a consumable test kit, so no manufacturer warranty period applies. That does not affect your rights under the Australian Consumer Law: if the product is faulty, unsafe or not as described, you are entitled to a remedy. Ships as standard freight.

Why does this kit measure in drops instead of giving me a test count?

Because it's a titration test – you add reagent until the colour changes, and the number of drops is the answer. Harder water needs more drops per test, so the exact number of tests you'll get from a bottle depends on your own water, not a fixed figure API can print.

What's the difference between GH and KH?

General Hardness (GH) measures dissolved calcium and magnesium – the minerals many fish and plants need. Carbonate Hardness (KH) measures carbonate and bicarbonate, which buffer pH and stop it swinging with every water change or CO2 dose.

My KH reads very low. Does that matter?

Yes – low KH means little buffering capacity, so pH can swing quickly with small changes in the tank. If you're also seeing pH drift, low KH is often the underlying cause.

Does this kit work for saltwater and reef tanks too?

API rates the reagents for both fresh and saltwater, though reef keepers chasing precise alkalinity for coral growth often prefer a dedicated marine alkalinity test alongside this one.

How do I convert degrees to ppm?

The instruction sheet included in the box carries a conversion table from °dGH/°dKH to ppm. We haven't reprinted the exact conversion figures here, since we could not independently verify them from API's own published documentation.