Don't add ice from gas stations or other retail places because it usually has chlorine and other chemicals in it.
Here's what I do. At the end of the day I'll usually take 3 or 4 empty water/gatorade bottles and fill them 3/4 full with lake water. Take them home and add 1 teaspoon of "Please Release Me" or "Rejuvenate" and then put in the freezer. Put them in your cooler the next time your heading to the lake. When you go to put them in the livewells just take off the lids and drop them in. It cools the water and add the chemicals needed to keep the fish healthy and lively.
Give it a try.
Charlie