I've been involved with freshwater ponding for a while and some people there are also having problems with dinoflagellates.
The common theme between fw and sw seems to be aquatic environments where people are trying to micromanage water quality, which usually ends up in an unhealthy and unsustainable aquatic environment.
Our reef keeping hobby is subject to micromanaging by it's nature, so that makes it pretty susceptible to dinoflagellates..
In freshwater ponds, some people are using a copper ionizer which kills off populations of algae. Dinoflagellates increase in population as a result because the main nutrient nitrogen remains.
Local oxidation will temporarily kill off dinos because they are organic, but the long term solution seems to be increasing the diversity of various algae.