Mosquito Dunks by Summit

We have a small water feature in our garden, so for the second year I am adding one of these periodically. They certainly do seem to keep the mosquito population under control. My only quibble would be the claim that one lasts for “30 days or more.” They absorb water and presently begin to break apart. Perhaps the active ingredient remains in the water even after that? Don’t really know, so once the dunk is entirely reduced to just floating debris, I scoop that out and add another. That means the six-piece card doesn’t equal a six-month supply. Possibly this is just my misunderstanding, however.