One of the most common mistakes in guppy keeping is treating every white mark as ich. Ich is common, but so is columnaris (a bacterial issue that can present as pale patches, “cottony” areas, or fuzzy mouth/fin edges). The reason this matters is simple: the wrong treatment can make the real problem worse.
How ich usually looks
Ich typically appears as many tiny white dots that look like grains of salt sprinkled across fins and body. Fish often flash (scratch) against objects, and the outbreak tends to spread across multiple fish over a short period.
How columnaris often looks in guppies
Columnaris can show up as:
- pale/white patches that are irregular (not “salt grains”)
- fuzzy edges around the mouth (“cotton mouth”) or fins
- saddleback look (a pale patch across the back)
- rapid decline in a stressed fish after heat or water issues
It often hits fish that are already stressed from poor water, heat spikes, transport, or crowding.
Why the mix-up is dangerous
Many ich approaches involve raising temperature. Heat can speed up the ich life cycle (helpful), but it can also accelerate bacterial growth and reduce oxygen — which can worsen columnaris. If you crank heat aggressively and the real problem is bacterial, you can push fish over the edge.
What to do first (for either condition)
- Increase oxygen (surface agitation / airstone).
- Test ammonia and nitrite (both should be 0).
- Stabilise temperature (avoid sudden jumps).
If you’re confident it’s ich
Treat per label and keep oxygen high. Mild temperature increases can help, but don’t overdo it. Consistency beats extremes.
If you suspect columnaris
Focus on clean water, oxygen, and targeted antibacterial treatment if progression continues. Keep temperature stable rather than hot, and avoid piling multiple meds at once. If possible, isolate the affected fish so you’re not dosing the entire display unnecessarily.
The key takeaway: don’t treat symptoms blindly. A quick diagnosis check saves lives, saves money, and avoids the “I treated it and everything got worse” spiral.
