You can probably use a bucket near unpolluted areas if you go out a way from shore. I use seawater collected near Bodega Bay, CA (Just north of SF/ Point Reyes) for my nano, and I will never go back to artificial saltwater. I just let it warm up to room temperature (tank temperature) and dump it in. It's been filtered through a pretty coarse floss filter, I assume, but there are still copepods and other critters present. I've never seen my corals look so great. It might be that they're getting natural plankton, some element not found in the artificial mixes, I'm not sure, but they look a whole lot better.
