Suspected household fumes or spray reaching the tank
This looks like: airborne chemical absorbed through the water surface
Why this happens
Many aerosols leave oily films that block gas exchange and carry solvents. Fish lack kidneys like ours — they absorb what touches the gills fast.
How sure are we? Hard to prove without lab testing, but timing after sprays or incense is a strong pattern.
What to do right now
- Stop using products in the fish room immediately — move tank maintenance away from fragranced air.
- Remove surface film: gentle paper towel skim or increased ripple; large 30–40% water change with matched, dechlorinated water.
- Run carbon in the filter temporarily if you already own media rated for aquariums — replace after a few days.
- Keep lids slightly vented unless you jump kids or cats — stale air beats perfume.
- Watch survivors 48h; note what was used for the vet or retailer if losses continue.
What not to do
- Don’t blast essential oil diffusers beside open tanks.
- Don’t “detox” with random salts — fix source and water first.
If that doesn’t fix it
If fish still crash with pristine habits, test ammonia and inspect heaters for stray voltage.
Catch this earlier next time — log your water parameters in App-aquatic. Free forever.