Tap Water: Friend or Foe?

To us, tap water is clean and safe. To a fish, it is a chemical bath that burns gills and destroys slime coats. This is because municipalities add disinfectants to kill bacteria in the pipes.

The Two Disinfectants

1. Chlorine ($Cl_2$)

• What is it?: A gas dissolved in water. It is volatile and evaporates naturally.
• Removal:
  • Aging: Letting water sit in a bucket for 24 hours (with an air stone) will gas off 99% of Chlorine.
  • Chemicals: Standard dechlorinators work instantly.

2. Chloramine ($NH_2Cl$)

• What is it?: A combination of Chlorine + Ammonia. It is stable and does not evaporate.
• Removal:
  • Aging: Does NOT work. You can age it for weeks, and it will still be there.
  • Chemicals: You need a dechlorinator specifically designed to break the Chlorine-Ammonia bond (like Prime or Safe).

Why This Matters

If you add untreated tap water to your tank:

1. Biological Genocide: Chlorine kills bacteria. It will wipe out your beneficial filter bacteria, crashing your cycle.
2. Gill Damage: It chemically burns the delicate gill filaments of fish, causing suffocation.

Water Change Best Practices

1. Treat the New Water: Add conditioner to the bucket before pouring it into the tank.
2. Treat the Whole Tank: If you use a hose (Python system) to fill directly from the tap, dose enough conditioner for the entire tank volume, not just the water you added.
3. Temperature Match: Ensure the new water is within 2°F (-17°C) of the tank water to prevent shock (and Ich).

RO/DI Water

Reverse Osmosis / Deionized water is 100% pure $H_2O$. It has:

• 0 ppm Chlorine
• 0 ppm Ammonia
• 0 KH / 0 GH

Warning: You cannot use pure RO water alone! It has no minerals (GH) or buffer (KH). You must "remineralize" it with products like Equilibrium or mix it with tap water.