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.
How sure are we? Moderate until you see the pattern — pictures beat guessing.
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.
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.