Your quoted source "A man has died and his wife is under critical care after the couple, both in their 60s, ingested chloroquine phosphate, an additive commonly used at aquariums to clean fish tanks." doesn't actually say these particular people used a fish tank product as their source of chloroquine phosphate.

This comment is harshly worded but explains the subtly well: https://news.ycombinator.com/item?id=22670152