Scratching on rocks / flashing
This looks like: external parasites — ich, velvet, or flukes are the big three
Why this happens
Skin irritation makes fish scrape. Different bugs look different up close — ich dots vs velvet dust vs flukes that favor gills.
What to do right now
- Shine a phone light sideways — velvet can look gold-dust, not white salt.
- Raise observation first — carbon out if you medicate later so treatments work.
- Confirm species tolerances — scaleless fish need half doses of some meds.
- Treat the whole tank if one fish shows ich; parasites rarely stay polite.
- Pause carbon-heavy fad gadgets; increase temp only where classic ich treatment guides match species max.
What not to do
- Don’t confuse fluff fungus on wounds with ich dots.
Stop it happening again
Quarantine new fish and plants, keep water quality high, and avoid the temperature swings that let parasites take hold.
If that doesn’t fix it
Jump to white-spots-ich if you see discrete grains on fins or body.
Catch this earlier next time — log your water parameters in App-aquatic. Free forever.
This isn't veterinary advice - it's a directional read to help you decide your next step, based on the most common causes. We can't see your fish, so pair it with a liquid test kit and clear photos, and see an aquatic vet or a trusted local fish shop for a valuable or seriously ill fish.