In a nut shell, redox is your waters ability to hold disolved oxygen. It is more commonly referd to as ORP or oxygen reduction potential. A good orp level for most systems is about mid 300 mlqv although higher values are not uncommon. (I maintain my saltwater fish system at 400 to 425 mlqv in my sump). THe most common way to raise your ORP level is with the use of ozone injection into a reactor or a protien skimmer. I use a large ozone genorator and a controller to monitor my orp value and inject ozone into my protien skimmer as needed to maintain the orp value I want. THere are other things that will raise your opr value as well (large water changes for example or a good sized U.V. sterilizer) but all the ways that raise orp are normally very temporary or have little affect. I think adding hydrogenperoxide to your water is a method that I have readabout that some people use to raise orp but I have never personally done this.
Joel