Dark Elixir Storage at Town Hall 9: max level 6. At Town Hall 18 the cap is level 13. It unlocks at Town Hall 7. Max level per Town Hall: TH7 2, TH8 4, TH9 6, TH10 6, TH11 6, TH12 7, TH13 8, TH14 9, TH15 10, TH16 11, TH17 12, TH18 13.
Tap a Town Hall to open this item there. Dashed: not available at that Town Hall yet.