Goldfish Death After Pond Cleaning: Water Change Shock

Sequence

2-ft deep Phoenix pond, 9am–3pm sun. 3 feeder goldfish + small koi added. 2 died week 1. Survivor thrived. 75% water change (hosed rocks, refilled). Fish gasped, died in 30 min. Plants repotted with dirt exposed.

Causes

1. 75% water change = massive shock: Chemistry, temperature, oxygen, chlorine/chloramine all changed instantly.
2. Exposed dirt: Clouds water, clogs gills, may leach alkalinity (AZ clay is alkaline) or contaminants.
3. Heat: 100°F+ water holds little oxygen. Waterfall helps but not enough after large change.
4. No dechlorinator: City water has chloramine (standard dechlor doesn't remove).

Correct Cleaning

• Never >20% water change at once.
• Vacuum debris instead of draining.
• Pot plants with aquatic soil + pea gravel cap.
• Always use chloramine-removing conditioner.
• Test pH, ammonia, nitrite after any work.

Murky Water Fix

Green = algae (add plants, UV). Brown = tannins (carbon). White = bacterial bloom (wait). Don't large-change.