dKH (degrees of Carbonate Hardness) measures the buffering capacity (alkalinity) of aquarium water, specifically the bicarbonate + carbonate concentration. Higher dKH = more resistance to pH swings.
Practical use in aquariums
Reef tanks target 8-12 dKH (most stable at 8-9 dKH). Freshwater planted tanks run 3-8 dKH typically. Test with a Salifert or Hanna alk checker; swings of more than 1 dKH per 24 hours stress coral.
How dKH fits the bigger picture
Understanding dKH matters because it's connected to broader husbandry decisions: water chemistry is the foundation of every other aquarium parameter - chemistry mistakes show up months later as livestock loss.
Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.
Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.
Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.
Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.
Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.