We had a garden hose we used specifically for change outs of water for our 50 gallon tank, which we had goldfish. It was accidentally used to spray the yard with weed killer, then we used it for change out.
A half dozen fish died overnight after 25% water change. The rest did not look good. We pulled them out and put in bowls, where they started looking great. We noticed an oil slick on the water and cleaned out everything in tap water several times, gravel, tank, pump and put in new cartridges. We ran everything through for about a week. Meanwhile, fish completely recovered. We put them back in and immediately they slowed down, not doing well. After a day, they got white pus around gills and oil slick appeared on water again. Again, we took them out of tank and put in bowls, where they started doing better, no pus on gills. So, we bought a new 20 gallon tank, recleaned the small rocks, and put in a few items from old tank that had been cleaned, with plain water several times.
Put the fish in after several days, and they died within a couple hours. Bought new batch, died overnight. Do I give up on whole thing and buy new everything? Is there a sure way of removing the weed killer?