Water Parameters

What is a good level of KH in a planted aquarium ?

What is a good level of kH in a planted aquarium ?

CARBONATE HARDNESS KH

Carbonate hardness, is a measure of water hardness caused by the presence of carbonate (CO3) and bicarbonate (HCO3) anions.It is a measure of the water’s buffering capacity; the higher the KH, the higher the pH in absence of other chemicals in the water, and the more resistant the water is to downward fluctuations when an acid is added.

Pure distilled water that has 0 KH, and 0 other amounts of acid/bases will have a pH of 7. As KH increases, the pH will increase as well. KH has no innate value to most plants (some plants can use carbonates as a Carbon source and will grow better in higher KH water when deprived of other carbon sources, but this is very energy intensive for the plant). It’s sole purpose if any, is as a buffer to prevent tank water from getting overly acidic. Bacteria consumes it in small amounts as part of the ammonia oxidation process.

✅ 

Ideal KH Range: 3–8 dKH

This is equivalent to 53.6–143 ppm (parts per million as CaCO₃).

🔍 Why This Range Works Well:

  • 3–5 dKH is ideal for CO₂-injected planted tanks. It provides just enough buffering to prevent dangerous pH swings while allowing CO₂ to drop pH effectively for plant uptake.
  • 6–8 dKH is better for tanks without CO₂ injection, or for aquariums with more sensitive livestock that need slightly more stable water chemistry.

💡 Key Considerations:

  • Lower KH (<3 dKH) can lead to unstable pH, especially in CO₂-enriched tanks. This can stress fish and plants.
  • Higher KH (>8 dKH) can limit plant access to nutrients, especially iron and other trace elements, due to pH staying too high.
  • If you are using RO or distilled water, KH will be very low, so you may need to add a remineralizer like aquaLife’s GH/KH boosters.
  • Plants like Glossostigma, Hemianthus callitrichoides, and Rotala species prefer slightly softer water (KH 2–4).
  • Some species, like Valisneria, may prefer higher KH and more alkaline conditions.

🧪 Related Targets:

  • pH: Aim for 6.4–7.2, depending on whether you’re injecting CO₂.
  • GH (General Hardness): Typically 4–8 dGH is a good target to support both plants and livestock.
  • CO₂: Around 20–30 ppm for optimal plant growth in CO₂-injected tanks.

🛠 How to Adjust KH Safely

✅ Products for 

raising

 KH / buffering

  • Use a remineraliser or KH/alkalinity buffer if KH is too low.  
  • Natural ways: add small amounts of limestone, dolomite, crushed coral in filter or substrate (slow release). 
  • Seachem Alkaline Buffer 300 g — Raises KH/pH via carbonate/bicarbonate buffering. Link  
  • NeoTiger KH+ / GH+ 250 mL — Designed for soft or RO water setups to establish mineral balance (including KH) for shrimp/plant tanks. Link  
  • Seachem Equilibrium 300 g — Although marketed more for GH (general hardness), the product description mentions “To maintain KH, we recommend Alkaline Buffer.” Link  

🔻 Products for 

lowering

 KH / buffering toward softer water

  • Seachem Acid Buffer 300 g — A non‑phosphate buffer designed to lower pH and in doing so, converts carbonate alkalinity (KH) into available CO₂. Link  

💧 RO / Soft‑Water Units (for very low KH baseline)

When you want a very low‑KH (and low other dissolved minerals) base water — e.g., for soft‑water planted tanks or specific biotope setups — RO/DI systems are ideal. Seven Ports carries these units under the brand AquaLife (AquaLife / Aquarium Life Support Systems) and offers guidance on their use.

  • AquaLife 3‑Stage Dolphin RO Unit 100 GPD — Includes 1‑micron sediment filter, carbon block, and TFC RO membrane. Link  
  • AquaLife 4‑Stage Barracuda RO & DI Reef Tank Unit 100 GPD — A 4‑stage RO + DI (deionization) system for even purer output. Link  
  • “the AquaLife RO units are the best quality …”  

🎯 How to use the products in your KH strategy

Once you have a low‑KH base (via RO/DI), you can add exactly the KH you want (using KH‑raising products) — this gives you maximum control for planted aquariums.

If your tap/KH is too low for your plants/fish, use Alkaline Buffer or NeoTiger KH+/GH+ to raise KH gradually.

If your KH is too high (and you want to lower it) or you’re using very soft‑water biotopes: either use RO/DI water as a base (with the AquaLife units) and then remineralize to your target, or use Acid Buffer to reduce KH somewhat (but note: lowering KH chemically can be more tricky).