Anything above the mid to high 70's in surface temp usually got me turning the pumps onto manual for tournaments, especially if I caught some keepers early. I rarely used ice. It takes a lot of ice to do a good job and fast water temperature changes of 10 degrees or more can also kill bass at times.
You can fill from the coolest water you find and then recirc with some ice and the CORRECT amount of Catch and Release or Please Release Me but studies have shown that bass in a livewell longer than 6 hours have a much lower survival rate. You really should change your water out somehow somewhere in a manner that won't shock the bass (big water temp difference or other possible water quality changes).
My practice was to always keep my great big Ranger livewells full of fresh water and occasionally add a small capful of one of the above chemicals. If I was leaving cooler water to enter much warmer water and/or water that was remarkably different (example: Lake St. Clair back into the Metro Beach launch with a livewell full of big smallies [hopefully
]) I closed the wells off by putting the valve on recirc out in the lake, adding chemicals and capping off my outflow with a couple pill bottle caps. I always did this for long runs. Especially in rough water. I'd rather have a wet back deck than dead bass. I stopped several times on the way in and checked, adding more lake water if necessary.
Since my boat is a 1993, I didn't have some of the fancier, new systems so I added my own 3-way valves to get recirc and also added a bubbler designed at the time for livewells, using the smallest pored stones because the bubbles only work if the oxygen from them can be absorbed into the water. If they all bubble up to the surface fast without any absorption, it's just another 'make the angler feel good but do nothing for the fish' action. If I fished tournaments now, I would probably look at some type of oxygen adding system, putting in the one that best appears to actually add oxygen molecules into the water that fish can actually breathe.
On inland lakes with the heat we've had this year, if I was fishing tournaments I might start going the ice route but only with a small amount of chemical too and making sure I did not shock the bass by too drastic a water temp change.
Over the years, I often got compliments from tournament directors about the health and vigor of my weighed in bass. I really believe we should do as much as possible to let the bass go as close to the shape we caught them in, or not fish bass tournaments. Too much at stake. Especially in some of the Northern, 'not bass tournament-friendly states.'
