Hi . I have a problem with some fish dying . I have some gubbys swordtails mollies amongst others . My black Mollie showed signs of trouble and died . Yesterday a gold one started the same . It was nearly dead . So yesterday morning I filled a bucket of tap water . Treated it as usual and put him in there just to see if it would help . We went away for the day and when we got home I expected him to be dead . But he was back full of life !I put him back into tank last night but hes in trouble again this morning. Tank water tested fine . Help ?