Fine bubbles rising through a column of clear aquarium water, green plants soft behind the glass.

Water Chemistry & the Nitrogen Cycle

The biology does the filtration. Ammonia becomes nitrite becomes nitrate that plants eat, and the whole loop runs on bacteria you cannot see. These are the guides to the nitrogen cycle, pH, hardness, and reading a test kit.

All 8 guides

Water Chemistry & the Nitrogen Cycle

Ammonia in a Fish Tank: Where It Comes From and How to Drop It

Ammonia is the first poison every tank produces, and 0.25 ppm is enough to burn a fish's gills. In a cycled tank you never see it. When a test shows it, the tank cannot keep up.

7 min read
Water Chemistry & the Nitrogen Cycle

Aquarium Tannins and Blackwater: What They Do

Tea-colored aquarium water is not dirty water. Tannins leach from driftwood and leaves, tint the tank amber, lower pH a few tenths, and suit the soft-water fish that evolved in them.

7 min read
Water Chemistry & the Nitrogen Cycle

Beneficial Bacteria: The Invisible Filter

The filter is a box of surfaces. The bacteria growing on those surfaces are the part that actually processes waste, and they take about a month to build.

7 min read
Water Chemistry & the Nitrogen Cycle

Fishless Cycling: The Humane Way to Start a Tank

Fish-in cycling asks an animal to live in rising ammonia for a month. A fishless cycle reaches the same finished tank with a bottle of ammonia and nothing alive to poison.

7 min read
Water Chemistry & the Nitrogen Cycle

GH and KH Explained: The Hardness Numbers That Matter

Two tanks at the same pH of 7.0 can be right for completely different animals, because pH hides the two numbers that decide it. GH and KH are those numbers.

7 min read
Water Chemistry & the Nitrogen Cycle

How to Cycle a Fish Tank (Before Any Fish Go In)

A new tank of clear water is one of the most dangerous places you can put a fish. Cycling builds the bacteria first, so the water is ready before anything lives in it.

7 min read
Water Chemistry & the Nitrogen Cycle

The Aquarium Nitrogen Cycle, Explained Simply

Fish waste becomes ammonia, ammonia becomes nitrite, nitrite becomes nitrate. Two colonies of bacteria run the whole conversion, and it takes about a month to build.

7 min read
Water Chemistry & the Nitrogen Cycle

What Is pH in an Aquarium, and Does It Matter?

Most fish care less about the exact pH number than whether it holds still. A stable 7.8 beats a 7.0 that drifts half a point a day.

6 min read

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