I just finished installing a 300-gal tub pond with 40-gal bog filter. I suspect water quality was low for a couple of weeks but is now good with full pond and running bog. However, my older fish - several 4-inch goldfish - started dying three days ago - obvious fin rot, clamped fins, and maybe other issues. My life is chaotic right now - no time to do close analysis - so I'm wondering if just a therapeutic dose of salt would be a good interim measure until I can devote more time to figuring out the problem? Or should I just wait to see if improved water quality will improve situation? Thanks for any advice.