Crude ash
Essential, indigestible substances
Crude ash
Essential, indigestible substances
There are many misconceptions about koi food. The biggest one is undoubtedly the idea that the crude ash percentage should be as low as possible. In this chapter, KiGen definitively debunks this assumption.
The crude ash content in KiGen food is higher than average. However, this is a deliberate and well-founded choice. The higher percentage is the direct result of essential additions that we consider vital for the health and vitality of koi. This includes salt, which makes up about 2.5% of the total food composition, and montmorillonite clay, a valuable mineral that is standard in all KiGen feeds.
Below is a complete and clear explanation of the function and importance of crude ash in high-quality koi food.
Crude ash
What does "crude ash" really mean?
Crude ash is NOT an ingredient, but an analytical measurement.
It is the residue left after the food has been completely burned (±550–600°C). Everything that doesn’t burn—minerals and inorganic substances—is measured as crude ash.
Important:
- Crude ash is not waste
- Crude ash is not harmful
- Crude ash = total minerals + inorganic components
It says nothing about:
- Digestibility of the total feed
- Quality of the protein source
Crude ash
Why is crude ash often wrongly seen as "bad"?
The reasoning many hobbyists use is understandable but oversimplified:
“Crude ash is indigestible > indigestible is ballast > ballast is bad > so crude ash must be as low as possible.”
This reasoning ignores one crucial point: Not everything that is indigestible is useless or harmful. In fact, for koi, certain indigestible substances are functionally necessary!
Crude ash
Examples of valuable substances that fall under crude ash
Salts and electrolytes (Na, K, Cl)
Sodium chloride (salt) is fully included in crude ash.
Functions in koi:
- Supports osmoregulation
- Reduces stress on the gills
- Relieves the kidneys
- Promotes slime coat production
- Improves recovery from stress or damage
Essential for health.
Calcium & Phosphorus (Ca / P)
Both minerals significantly increase the crude ash value.
Functions:
- Skeletal and scale formation
- Muscle contraction
- Nerve conduction
- Energy metabolism (ATP)
Too low Ca/P is harmful. Too high Ca/P can be problematic.
Balance is crucial, not the lowest possible crude ash.
Trace elements (Fe, Zn, Cu, Mn, Se)
All part of crude ash.
Functions:
- Enzyme activity
- Immune system
- Pigment formation
- Antioxidant effect
These substances:
- Are often only present at ppm levels
- Still contribute measurably to crude ash
- Are indispensable
Montmorillonite clay
Properties:
- 100% mineral > 100% crude ash
- Indigestible
But functional:
- Binds toxins (mycotoxins, heavy metals)
- Stabilizes the intestinal environment
- Promotes stool consistency
- Supports the intestinal wall and microbiota
Classic example of a functional indigestible substance.
Silicates & trace element-rich ash components
In natural food (algae, biofilm, sediment particles), koi also ingest inorganic fractions.
Functions:
- Slow mineral release
- Intestinal stimulation
- Mimicking natural feeding behavior
When is a high crude ash value actually a problem?
Crude ash can be negative when:
- It mainly comes from:
- Cheap fillers
- Excessive bone meal residues
- Poorly balanced mineral mix
- It is not functionally justified
- It is accompanied by:
- Poor protein quality
- Low digestibility
- Overloading excretion
The problem is not the crude ash, but its composition.
The right way to look at crude ash
A better approach:
“What does the crude ash consist of and why?”
Crude ash is:
- A catch-all term
- Meaningless without context
- Only valuable when linked to function and source
Conclusion (short and sweet)
- Crude ash is not waste, but a collective term for minerals
- Indigestible does not automatically mean useless
- Many crucial substances for koi fall under crude ash
- A higher crude ash can be:
- Deliberate
- Functional
- Health-promoting
The quality and composition are decisive, not the percentage alone.
