Boat is a TR-21 with separate livewells. Pumps and recirc worked in both. Water temp 82. Within a 30 minute period of checking there were 4 dead fish in the port livewell and 5 alive in driver side. Any thoughts on what could have caused this? Contamination of some kind? If contamination, what is best way to decontaminate? I never ever have had a livewell issue like this.

Are you sure the recirc pumps worked, or you could just hear them both turn on?

Are you sure the recirc pumps worked, or you could just hear them both turn on?

Good question but I visually verified that recircs worked in each. First thing I thought of too.

Have they been cleaned recently? Had a similar situation a week ago when we lost 4 of 5 during a tourney. We noticed a strong ammonia almost like cat pee smell. The live well got cleaned and had some baking soda water recirculated through it and this weekend all was well.

Are they the same gph pumps?   Is one weakening?   If cartridge type I'd pop the pump out and see if there is any obstruction limiting flow.  Weeds in the intake screen?   Definitely clean the wells too.   I hate loosing fish, it sucks.

had to be contamination.  Clean and rinse with your pumps running.