Hi OrangeC, you have the dose correct at 500mg per 10 gallon. Treatment is done over 10 days with a large water change per day (generally 50% or better) and redosing for the entire volume of the tank (vs the water replaced). Some folks raise the temp to help simulate the appetite and feel the heat aids in killing hex etc.
In my experience metro does not seem to hurt the beneficial bacteria in your filter but best to keep a eye on your water parameters.
Pat