How to make water more alkaline

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To make your tank water more alkaline you need to add a solution which contains hydroxyl ions to your water.

Typically the most common solution used to do this cheaply is to use Sodium bicarbonate (Bicarbonate of Soda used in home baking) added to water. This will go up to a pH of 8.2.

Other solutions

To achieve a higher pH you need to use:

  • Potassium hydroxide (KOH) also called Potassium hydrate, calcinated or caustic potash[1]
  • Calcium hydroxide (CaOH) also called slaked lime, hydrated lime, Kalkwasser (Lime water), Calcium hydrate or pickling lime[2]
  • Sodium hydroxide (NaOH) also called lye or caustic soda (this is usually found in cleaning[3]
  • Sodium carbonate (Na2CO3) also known as Carbonic acid, Carbonic acid, disodium salt; Bisodium carbonate; Carbonic acid sodium salt; Disodium carbonate; Soda; Soda ash; Soda Ash[4]

Note these chemicals are corrosive with metal.[5][6][7][8]

Special notes

These chemicals are potentially dangerous to humans and fatal to aquarium life if used incorrectly. Please consult their MSDS sheet before using.


  1. MSDS Sheet for KOH
  2. MSDS Sheet for CaOH
  3. MSDS Sheet for NaOH
  4. Na2CO3 and its properties
  5. KOH and its properties
  6. CaOH and its properies
  7. NaOH and its properties
  8. Na2CO3 and its properties