Do you have multiple aquariums but don’t want to mix up separate batches of water for water changes? Why not make up one batch and do some water shuffling? Most hobbyists that have multiple tanks tend to have a primary reef aquarium that gets a majority of the attention and one or more secondary aquariums that are FOWLR tanks or soft coral reefs. The primary reef will require the most attention and the most pristine water, so it tends to get the water change with the new batch of saltwater. The water drained from the reef will still be far cleaner than that of the FOWLR and possibly even that of the softy reef, so it’s not a far stretch to say it would be suitable to perform a water change on the other aquariums with this water. This approach saves on aquarium filters, prevents excess water waste, and still manages to reduce the pollutants in the aquariums it is being used on.