I regularly expose my danios to 13-14C when I do water changes.
I have Danios dangila [8], roseus(6), sp hikari [8], glowlight(3), putao glowlight (3), feegradei (10), TW01 (2), TW03 (6), rerio (40), abolineatus (40), kerri (10), pulcher (25), tweediei (40), kyathit striped (4), kyathit spotted...