This is what I would do. Use 500mg per 100L (26gal) twice a day. Metro breaks down in water.
Put the 500mg in a mortar and pestles to gind it into the finest powder possible. Mix in some tank water and make a slurry. Put a few food pellets in the slurry to soak up the medication.
Empty the whole lot into the tank rinsing out all of the medication. Those fish that eat will get a better dose.
Make sure your tank temperature is about 30 deg C - warmer than normal.
Do a 50% pwc on day 3. Treat for 5 days.
When all fish are eating, make a 3% solution of epsom salts. Use an eye dropper to drop this onto food pellets so they soak it all up. Feed this to the fish twice a day for 3 days.
When feeding, feed a lot less than you would normally. You want the fish to be really hungry to eat the treated food.
