I. Harm Mechanism of Elevated Ammonia Levels

1. Direct Toxic Effects
   Ammonia (NH₃/NH₄⁺) damages the epithelial cells of koi gills, obstructing oxygen exchange and leading to tissue hypoxia. At ammonia levels >0.5 mg/L, koi may exhibit gill filament congestion and increased mucus secretion. At levels >2 mg/L, it can cause spasmodic swimming or even acute death.
2. Compounded Metabolic Stress
   Ammonia poisoning impairs the detoxification functions of the liver and kidneys. The digestion process itself increases oxygen consumption and metabolic waste (e.g., carbon dioxide, urea). Continuing to feed during elevated ammonia levels creates a dual assault of "increased digestive oxygen demand + heightened ammonia toxicity."
   

II. Four Key Roles of Stopping Feeding

1. Cut Off External Ammonia Input
   Food residues and feces account for over 60% of ammonia sources in water. Stopping feeding can immediately reduce ammonia production by 50%–70%.
2. Reduce Koi Metabolic Burden
   After fasting, koi basal metabolic rate decreases by approximately 30%, lowering oxygen consumption and buying time for gill repair and detoxification.
3. Create Conditions for Water Quality Recovery
   During the fasting period, the following measures can accelerate ammonia degradation:
   • Immediately increase aeration (boost by 50%) to promote nitrification.
   • Add zeolite or ion-exchange resins to adsorb ammonia.
   • Supplement with compound nitrifying bacteria (ammonia-tolerant strains).
4. Prevent Secondary Infections
   Gill tissues damaged by ammonia are highly susceptible to secondary bacterial (e.g., Flavobacterium columnare) and parasitic infections. Fasting reduces koi activity and energy expenditure, allowing resources to concentrate on immune repair.
   

III. Emergency Response Protocol for Elevated Ammonia

1. Immediate Testing and Confirmation
   Use professional test kits to measure ammonia concentration, and simultaneously check pH (higher pH increases the proportion of toxic NH₃).
2. Tiered Response Strategy
   • Mild elevation (0.5–1 mg/L):
     Stop feeding for 24 hours, change 30% of the water, add zeolite powder (100 g per ton of water), and increase aeration to maintain dissolved oxygen >6 mg/L.
   • Moderate elevation (1–2 mg/L):
     Stop feeding for 48 hours, change 50% of the water, use sodium thiosulfate for detoxification (as per instructions), and add EM bacterial solution.
   • Severe elevation (>2 mg/L):
     Stop feeding for at least 72 hours, transfer koi to a backup pond, and thoroughly disinfect the original pond while rebuilding the nitrification system.
3. Criteria for Resuming Feeding
   When ammonia levels remain stable below 0.2 mg/L for three consecutive days, and koi exhibit normal swimming with no surfacing behavior, resume feeding with 30% of the normal amount of easily digestible feed (e.g., wheat germ-based). Observe for two days; if no abnormalities occur, gradually increase the amount.
   

IV. Long-Term Preventive Measures

1. Establish Correlation Monitoring Between Feeding and Water Quality
   Test ammonia levels 2 hours after each increased feeding to determine safe feeding thresholds.
2. Optimize the Filtration System
   Ensure biological filter media volume is ≥10% of total water volume, and regularly clean pre-filtration mechanical media.
3. Improve Feed Management
   Choose feeds with low ammonia excretion rates (protein digestibility >85%) and avoid overfeeding.