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WATER TESTING & MAINTENANCE

GH / KH Test Kit

Measures general and carbonate hardness — the numbers that decide which species you can keep.

Maintaining stage Water
Unplug before servicingHands out of the water firstDrip loop on every cableTest before you dose30 ppm CO₂ ceilingCycle before stocking
WaterTechnical line drawing of GH / KH Test Kit
Specification
MethodDrop-count titration
GH reagentRed → green endpoint
KH reagentBlue → yellow endpoint
Resolution1 dGH / 1 dKH per drop
Tests per kit75–150 each
UnitsdGH / dKH, or ppm (×17.8)
Technical parameters
Soft-water tank GH2–6 dGH
Community tank GH6–12 dGH
Shrimp tank GH6–10 dGH
KH for stability≥ 3 dKH
KH with aqua soilDrops to 0–1 — watch pH
Test frequencyMonthly, or weekly when adjusting

GH and KH are two different measurements that are frequently confused. General hardness (GH) is the total concentration of dissolved calcium and magnesium, expressed in degrees or ppm. Carbonate hardness (KH) is the concentration of carbonate and bicarbonate ions, which is what buffers pH against change.

Both matter, for different reasons. GH determines whether shrimp can moult successfully and whether plants can take up calcium — a GH below 3 dGH causes moulting failure in Neocaridina shrimp and curling, distorted new leaves in plants. KH determines how stable pH is: a tank with KH of 1 dKH has almost no buffer, and the pH will swing with every water change, every CO₂ adjustment and every addition of aqua soil.

The two are measured the same way — counting drops until the sample changes colour — but with different reagents and different colour endpoints. GH is usually a red-to-green transition and KH a blue-to-yellow one. Counting drops is genuinely accurate enough, provided you shake between drops.

Safety and welfare
  • Aqua soil and CO₂ injection both deplete KH. A tank that starts at 5 dKH can reach 0 within weeks, and at that point pH is unstable and dangerous. Test regularly.
  • Do not adjust hardness with a single large dose of remineraliser. Raise GH by 1–2 degrees at a time, over days, or shrimp will fail their next moult.
  • Hardness changes must be matched in water-change water. A 50% change with water 4 dGH different is a shock, not a change.

Using it well

Write your source water GH and KH on a label inside the cabinet. It is the baseline everything else is measured against and it changes seasonally.
If GH is fine but KH is zero, you can raise KH alone with potassium bicarbonate. It adds buffer without adding calcium.
Test the water you are about to add during a water change, not just the tank. A mismatch there is the most common cause of a mystery crash.

Test alongside

pH test kitNitrate test kitAqua soilCherry shrimp
Note. Parameters are conventional ranges across the category, not the claim of any one manufacturer. Nothing on this page is for sale and no outcome for any plant or animal is guaranteed. Simulator output elsewhere on this site is a simplified model, not a measurement — confirm everything with a test kit and the equipment's own instructions.
Related

Works alongside

pH Test KitWaterNitrate Test KitWaterAqua SoilSubstrateCherry ShrimpPlants