The foam is an aquarium problem that is addressed with a "protein skimmer". It is the result of churned water full of fish waste, dead fish, etc. Always examine bait tanks and avoid any that show foam at all and/or unremoved dead bait. Sounds like the original problem was bait from a sloppy operation that were then overcrowded. IOW way too many minnows for the container and many of them already dying when they were purchased.