Husband made seafood chowder 2 days ago, it now has a lemony taste; don't know why as lemon was not used. Anyone have an answer as to why?

Another way to cool it down uses soda bottles . Fill an empty bottle with water and put it in the freezer. Then use them as ice cubes. More smaller ones are better than a larger one.

Were any herbs used? Thyme--some varieties--can have a lemony taste, especially after allowed to steep.

Did you rapidly cool it after cooking it? It may have spoiled in the cooling down. Soup needs to cool to 40F within 4 hours to not spoil. I cool my soups by submerging the pot I cooked the soup in in a cooler filled with ice and water. Other than that, if you cooked it in aluminum or stored it in aluminum, even though there is no lemon in the chowder, any acidic element could've reacted with the aluminum to give it an off taste.