Understanding pH: The Acid-Alkaline Balance

pH (Potential of Hydrogen) is a measure of how acidic or basic (alkaline) your water is. It is one of the first parameters new hobbyists learn about, but often the most misunderstood.

The Logarithmic Scale

The pH scale ranges from 0 to 14:

• 0 - 6.9: Acidic (Lemon juice is ~2)
• 7.0: Neutral (Pure water)
• 7.1 - 14: Alkaline/Basic (Bleach is ~12)

Crucial Fact: Valid pH is a logarithmic scale. This means a pH of 6.0 is 10 times more acidic than 7.0, and a pH of 5.0 is 100 times more acidic than 7.0. Small changes in the number represent massive changes in the water chemistry!

Why pH Matters for Fish

Fish have evolved over millions of years to thrive in specific water conditions.

• Acidic Water Fish (pH 5.5 - 6.8): Tetras, Discus, Bettas, Rasboras (often from Amazonian waters).
• Alkaline Water Fish (pH 7.2 - 8.5): African Cichlids, Livebearers (Guppies, Mollies).

If you put an acid-loving fish in alkaline water (or vice versa), their internal osmoregulation works overtime to maintain balance. This causes chronic stress, reduced immunity, and shorter lifespans.

Stability > "Perfect" Numbers

Unless you are breeding sensitive wild-caught species, stability is far more important than hitting an exact number. Most captive-bred fish are adaptable. A neon tetra can live happily in 7.2 pH. However, if that pH swings from 7.2 to 6.2 and back within a day (a "pH swing"), the osmotic shock can kill them.

Do not chase the dragon of a "perfect" 7.0. It is better to have a stable 7.4 than a pH that bounces around.

How to Adjust pH (Safely)

To Lower pH (Make more acidic):

1. Driftwood / Almond Leaves: Must decompose to release tannins. Safe and natural.
2. CO2 Injection: High-tech method for planted tanks.
3. Active Substrates: Soils like Aqua Soil buffer water to ~6.5.
4. RO/DI Water: Mixing pure water with tap water.

To Raise pH (Make more alkaline):

1. Crushed Coral / Limestone: Add to your filter or substrate. Dissolves slowly.
2. Baking Soda: (Use with caution!) only for short term or specific recipes.
3. Alkaline Buffer: Commercial products focused on KH.

The pH / KH Relationship

You cannot easily change pH without considering KH (Carbonate Hardness). KH acts as a "buffer" or a shield for pH.

• High KH: pH is "locked" and hard to change.
• Low KH: pH can swing wildly (crash).

Always test KH before attempting to alter pH!