Check Mite with formic acid? How do the bees handle such and onslaught? The cure might be as bad as the disease.
First I quit using hard chemicals like Check Mite for the obvious reason, they don’t work like they once did because of resistance and long term contamination of comb. The best defense against varroa is not to let them build up to economic threshold which usually will cause the hive to crash no matter what you do, like declare total war by bombarding them with multiple chemicals none of which is consequence free, there is a trade off.
Many successful beekeepers don’t us any hard chemicals or soft chemicals like formic acid, read some of the articles in American Bee Journal from guys like Randy Oliver. If you wait until there is heavy mite load before you do mite treatment you are setting yourself up for failure more than success.
The Busy Bee teaches two lessons: One is not to be idle and the other is not to get stung.