How to make water more alkaline
From The Aquarium Wiki
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.
To achieve a higher pH you need to use:
- Potassium hydroxide (KOH) also called Potassium hydrate, calcinated or caustic potash
- Calcium hydroxide (CaOH) also called slaked lime, hydrated lime, Kalkwasser (Lime water), Calcium hydrate or pickling lime
- Sodium hydroxide (NaOH) also called lye or caustic soda (this is usually found in cleaning
- 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
These chemicals are potentially dangerous to humans and fatal to aquarium life if used incorrectly. Please consult their MSDS sheet before using.