I have been asked this question a 100 times. I have buddies that are fish biologists and former employees of the TWRA and other fish organizations.
There are two (2) different formulas that I use that have both been proven to be very successful and have posted them on many other sights and recieved praise after they have been tried and proven to work.
The 1st one is for cooler water conditions 70' dgrees or cooler.
Catch and Release, Please Release Me, Rejuvenate, all work at different prices.
All based on average 15-20 gallon livewells
1) Please Release me 2 cap full (1 cap full Rejuvenate if used)
2) Pickling salt or bakers salt from any grocery store (non iodized) 2 table spoons
3) 3 oz peroxide
4) (Summer time conditions) 1 Bag of ice per livewell or if you prefer make your own blocks of ice for summer water temps over 70 which is what I do.
5) Close livewells and add water to 3/4 full before ever leaving launch site area and add chemicals and go fishing. First ride mixes all together.( and in summer melts ice thus cooling water down to slow down fish). Don't ever add any more water the rest of the day. Use Pro-Air and or Recirculation units to keep water oxygenated. Peroxide will help prevent any infections from handling of fish and also helps promote O2 with Pro-Air or recirculation units. Please Release Me will also help fight infections and also at same time sedates fish by coating gills preventing them from banging around in livewells and also promotes slime coats. Always try not to let fish lay on floor of boat as it removes alot of the slime coat from the fish. (That is why I have never approved of BASS allowing fish to be flipped over into floor of boats rather then allowing wet nets to hold fish off floor.) After placing fish in live well it is good to check on fish in about 5 minutes to make sure it does not have bladder problem and is up right in live well. Remember your looking at possible money winnings so check on your fish often. When you arrive back at weigh in Pump the water out of your live wells or open live wells and fill bag with Livewell water to again help protect fish while waiting in line to weigh fish.. Sounds like a lot of work but it all only takes about 5 minutes to do once you develope a system of doing it. Also remember that you are trying to protect a creature that you enjoyed catching and might enjoy catching again. I have been using this formula for about 10 years and am proud to say that I have only lost 7 fish in all that time and all of those fish were deep hooked beyond help and none of them were big fish.
ADDED WARNING: I know many folks probably never give thought to this so I will add it. If your standing in line waiting to weigh in your fish never allow your bag of fish to rest on hot pavement or concrete in parking lots. Set it on your feet or have partner help you hold bag. I have seen entire bags of fish killed by anglers not thinking about how hot that pavement is in summer and cook a bag of big fish. Black Bags are the worst ones to do that with. Believe me you will not find an advocate for protecting Bass more than I.