Foz Down

[George]

Originally Posted by Frogger

I believe Fozdown is Lanthanum chloride. You may want to do a search on Lanthanum chloride in reef tanks. There are some risks associated with the use of this chemical as the precipitate lanthanum phosphate could be toxic to some fish and corals if not managed carefully.

Wrong info. Precipitation from Lanthanum chloride is not toxic. What happens is that the precipitation is so small, less than 5 microns, that it can cause irritation on the gills of some fish.
With the precipitation being so small, it's likely that it will be blown around in the tank instead of settling down so vacuuming is probably useless. Many people do 1. use a 5 micron filter sock to hopefully filter some of the precipitation. 2. Do a water change after a dosing because Lanthanum chloride reacts with phosphate instantly so you don't need to wait. 3. don't care and don't do anything since it's so small you can't see it anyway.
If you do decide to use Lanthanum chloride, go slow. This stuff works on lowering phosphate and works quickly. Sometime too quick