When the water temps reach 80 degrees, I fill the live early and always carry a few frozen water bottles (ozarka, auquafina, walmart, etc) and when I catch the first fish I place one bottle in the well, at mid day I place another and just before weigh-in I put another in. The second of these bottles is treated with Rejuvenate. I take the cap off the frozen bottle and as it melts in the well, it also despenses the chemicals. Never have any problems...!!! Never lost a fish...!!!
Some people add bag/block ice, but remember that ice was made from public water supplies and may have all kinds of additives like Chlorine and taste enhansers. I always use bottled water because it is pure water with no additives.
Hope this helps you to save some fish for your next weigh-in. My next Legend will have the Oxygenator as well.