Aquarium GH and KH FAQ: Hardness Buffering Test

GH (general hardness) measures dissolved calcium and magnesium; KH (carbonate hardness) measures the buffering capacity that keeps pH stable. Singapore PUB tap arrives at GH 2-4 and KH 1-2 — soft and lightly buffered, almost ideal for tetras and shrimp but problematic for African cichlids and high-tech planted tanks. This aquarium gh kh faq from Gensou Aquascaping at 5 Everton Park covers hardness science, and this guide answers the 10 questions Singapore aquarists ask most about GH and KH.

What is the difference between GH and KH?

GH is calcium plus magnesium content — what plants need for cell walls and shrimp need for moulting. KH is carbonate and bicarbonate content — what stops pH from crashing. They are independent: a tank can have high GH and low KH or vice versa. Most “water hardness” advice conflates them, which causes confusion.

What ranges do common species need?

Tetras and rasboras: GH 2-8, KH 1-4. Livebearers: GH 8-15, KH 4-8. African cichlids: GH 8-15, KH 8-12. Crystal shrimp: GH 4-6, KH 0-1 (RODI required). Cherry shrimp: GH 4-8, KH 2-6. Discus: GH 1-4, KH 0-2. Planted tanks generally: GH 4-8, KH 3-5 for stable CO2-driven pH.

How do I raise GH and KH?

Crushed coral, aragonite or coral chips in the filter raise both slowly. Seachem Equilibrium raises GH only. Salty Shrimp Bee Shrimp Mineral GH+ raises GH alone for crystal shrimp. Seachem Malawi/Victoria Buffer raises both for African cichlids. The water care category stocks these mineralisers.

How do I lower GH and KH?

Mix tap with RODI water at a ratio that hits target — for GH 3, mix 50:50 PUB tap with RODI. Peat moss in the filter binds calcium and lowers GH gradually. Indian almond leaves and driftwood lower KH through tannin acidification. The cleanest method is dilution with RODI.

Why does KH matter for pH stability?

KH is the chemical buffer that absorbs acid before pH drops. With KH under 2, every fish-respiration carbonic acid molecule pushes pH measurably down. With KH at 4-6, the same load barely moves pH. CO2-injected planted tanks need KH 3-5 to prevent crashes; below 2 dKH, CO2 systems become risky.

Does Singapore tap need adjustment?

For most community tanks, no. PUB tap GH 2-4 KH 1-2 supports tetras, rasboras, gouramis, corydoras and bettas without issue. Adjustment is needed for African cichlids (raise both), Caridina shrimp (RODI plus remineraliser), and CO2 high-tech tanks (raise KH to 3-4). Test once a quarter to track PUB drift — values shift 1-2 dGH across the year.

What test kit do I need?

API Freshwater Master Kit does not include GH or KH — buy the API GH and KH Test Kit separately at SGD 25. Salifert GH and KH kits are more accurate for shrimp at SGD 35-45 each. Drops change colour at the endpoint; count carefully because each drop equals one degree of hardness.

Can I use coral chips in any tank?

No. Coral chips push KH up and pH up, which suits African cichlids but stresses tetras and shrimp. Use only in tanks targeting alkaline conditions. A small mesh bag in the filter outflow allows easy removal if hardness rises too high. Pair with proper filter media for graduated hardness adjustment.

Why do my plants show calcium deficiency?

Singapore’s GH 2-4 is too low for fast-growing plants — calcium deficiency shows as twisted new growth on stem plants and necrotic margins on Amazon swords. Dose Seachem Equilibrium at 1 tsp per 80 litres weekly, or use a remineraliser like Salty Shrimp Aquaristik Mineral. Target GH 5-8 for healthy planted growth.

Does aquasoil change GH and KH?

Yes, dramatically. ADA Amazonia II actively strips KH and GH for the first 3-6 months — the soil acts as a cation-exchanger pulling carbonate and calcium into its substrate matrix. KH can drop from 2 to 0 within weeks. This is why aquasoil tanks crash without remineralisation. Add Bee Shrimp GH+ at every water change to maintain GH 4-6.

Related Reading

• Aquarium pH FAQ
• Aquarium TDS FAQ
• Tap Water Aquarium FAQ
• Aquasoil FAQ
• Water Change FAQ