It's a good idea to add some Pink Stuff when you add water; it will keep the metal in the water, hopefully long enough for the CuLator to capture it.

I would recommend that you NOT discard the Culator. Unless it's heavily discolored or gummed up with skimmer goo, it still works. The manufacturer's 30 day deadline had, I believe, more to do with sales than function. Instead, tie the old bag to the ladder or something else, and put the new one in the skimmer. The Culator's are quite slow at 'gathering' the metals; the more bags you have in the pool, the better off you'll be.