normally I would think snake oil too but this stuff has worked, which surprised me. I have been using diatom bags for some time to no avail, daily water changes everything. For a start its a 2 hour job just to do a water change on this particular tank, plants are regarded as food and ugf gravel stones or wood are playthings.
I have a devious plan for this lot which will take time to set up but it will be done.