Multiple Koi Deaths: Tannins, Plant Fertilizer, and Gill Issues

Sorting the Clues

• White cottony spots: Fungus (Saprolegnia), not ich. Salt helps.
• Algae on body + welts + fin loss: Secondary infection on wounds (spawning, handling).
• Brown/red gills with "dirt": Bacterial gill disease or ammonia burn; "dirt" is necrotic tissue.
• Tannins: From leaves/wood, not dirt. Slight tea color is harmless.
• Plant fertilizer with nitrate: If koi ate it, nitrate poisoning possible.

Immediate Steps

1. Remove all fertilizer tabs.
2. Test ammonia, nitrite, nitrate, pH.
3. 30% water change + dechlorinator.
4. Add pond salt (0.05%) and KoiZyme.
5. Maximize aeration (waterfall + air stones).
6. Contact local koi club for a gill scrape.

Jumping/Gasping

Indicates low oxygen, gill damage, or parasites. Aeration and salt address the first two.