If your aquarium pH is drifting low or crashing, the real problem is usually low carbonate hardness (KH) — the water has lost its buffering capacity. Raising KH raises and stabilises pH at the same time.

Here is how to do it safely, and when you should not bother.

Best methods to raise pH

Crushed coral or aragonite. Add crushed coral to the filter or as substrate. It dissolves slowly, raising KH and pH gradually and stably — the best long-term method.

Mineral additives. Products like Seachem Equilibrium or a KH buffer raise hardness in a controlled way. Follow the label and test before and after.

Water changes. If your tap water is harder than your tank, regular water changes naturally raise pH.

Limestone or Texas holey rock. Aquarium-safe calcareous rock dissolves slowly to buffer the water — ideal for African cichlid tanks.

What not to use

Avoid bottled “pH Up” products for ongoing control — like pH Down, they cause unstable swings. Never add baking soda blindly; it raises KH but is easy to overdose.

When you should not raise pH

Most community fish tolerate pH 6.5–8.0, and stability matters far more than the number. Only deliberately raise pH for hard-water species like mollies, guppies, platies and African cichlids. Soft-water fish like tetras and bettas prefer it lower.

Frequently asked questions

How do I raise the pH in my aquarium naturally?

Add crushed coral or aragonite to the filter or substrate, or use aquarium-safe calcareous rock. These dissolve slowly, raising carbonate hardness and pH gradually and stably.

Why does my aquarium pH keep dropping?

Falling pH is caused by low carbonate hardness (KH), so the water cannot buffer the acids produced by fish waste and decaying matter. Raising KH with crushed coral stabilises it.

Can I use baking soda to raise aquarium pH?

It works but is easy to overdose and causes sudden swings that stress fish. Crushed coral or a proper KH buffer gives a safer, more gradual rise.

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— Jaqline Smalling, FishForever