Water Chemistry Made Simple

Fish can get used to a lot of different water. What they can't handle well are sudden changes. A fish that has lived its whole life at pH 7.6 is healthier at a steady 7.6 than at a pH that jumps between 6.8 and 7.4.

Why chasing numbers backfires:

• Products like "pH Up" and "pH Down" change the number quickly.
• Your tank slowly drifts back, so you add more.
• The water swings up and down, and every swing stresses your fish.

A better plan:

1. Test your water so you know where it sits.
2. Pick fish that are happy in water like yours.
3. Keep it steady with regular water changes.

Most fish sold today were raised on fish farms and are used to a wide range of water. For them, steady water matters much more than hitting a "perfect" number.

The big exceptions are ammonia and nitrite. Those should always be zero. You learned about them in The Nitrogen Cycle course.