GH, KH and TDS for beginners

Three numbers do most of the work in a shrimp tank.

A small planted nano aquarium with dark substrate, driftwood and dense green plants. — Dense planting and dark substrate, which is what you want. The plants are not decoration: shrimplets cannot eat prepared food and graze biofilm off leaves and wood instead. Photo by Christian Ang on Unsplash.

GH, general hardness

Calcium and magnesium. Shrimp need both to build a new shell every time they molt. Low GH is the most common preventable killer. The shrimp gets stuck partway out of its old shell and dies. Target 6-8.

KH, carbonate hardness

The buffer that keeps pH stable. At KH 0 your pH can swing overnight. Target 2-4. Don't chase pH directly. Set KH and pH follows.

TDS, total dissolved solids

Everything dissolved in the water, measured with a cheap pen. It's the fastest way to notice something drifting. Target 180-250.

The mistake almost everyone makes

Top off evaporation with RO or distilled water, never tap. Evaporation removes water and leaves the minerals behind. Top off with tap and you're adding more minerals to water that just got more concentrated. TDS climbs a little every week until something breaks. Use tap for water changes and RO only for top-offs.

And RO on its own is not "better" water. It's empty. Straight RO has no calcium at all and will cause failed molts. It's a starting point you remineralise, not a finished product.

Stability beats optimality

A colony thriving at GH 9 will do worse if you rush it to 7 than if you leave it alone. Change parameters over weeks, not days.