Look up formic acid on the internet, particularly a site "Mite-Gone". This is an amazing product that is naturally found in nature, as is oxalic acid. With formic acid (if done correctly) has no ill effects on bees. It is probably one of the best ways to combat some bee problems. You will see that it combats Varroa mites, tracheal mites, chalkbrood, wax moth problems and so on. It is worth looking into it and finding out if this is a product that you would like to use. There is a myriad of information on the internet and many suppliers. The pads release formic acid fumes, which is heavier than air and sinks to the bottom of the hive, the bees fan to get rid of these fumes and this kills the varroa mite quickly and efficiently. Search the internet, my best advice, and this is from an unseasoned beekeeper, who is doing her homework. Oxalic acid is good too, but I think formic acid is easier and activates and deactivates, depending on the bees activities with fanning in the hive. Meaning, if they are clustering keeping warm, the treatment is on hold, when they get busy and fan, the treatment goes off hold. If any seasoned beekeepers have a differing opinion, I would love to hear, as I am new mostly (only 2 years keeping bees) and I love advice from good sources.