Help! I think I have a coolant leak!

I got my 01 intrigue gls back in early sept. and I noticed that the coolant tank looked a little brown, but the fluid was fine. Over the past few weeks or so I 've noticed that the coolant level is below the "cold" when cold and below the "warm" when hot. Could there be a leak, as I think it has dropped since a bought it? I sometimes smell that fishy smell of coolant after driving, then idling for a few minutes. My temp needle is always between 1/4 and 1/2, going toward the upper part of that range only when idling for a few minutes. Has anyone dealt with a 3.5L coolant leak? If so, was it as bad as the dex-cool issues with the 3.4 and the gaskets?

Check the carpet on your passenger side, if your smelling coolant inside the car it could very well be your heater core. It is located underneath your dash and when it leaks it will get inside of you car.

No, there is nothing on the floor. It's perfectly dry.