'algae-controlling' is a modern English compound formed from 'algae' and the present participle 'controlling'. 'Algae' comes from New Latin 'alga' meaning 'seaweed' (from Latin), and 'control' comes via Old French and Medieval Latin from elements meaning 'counter roll' or 'check'.

'algae' entered scientific/modern English from New Latin 'alga' (plural 'algae'); 'control' developed from Old French/Medieval Latin roots (e.g. contrerotulus) into Middle English 'control' and later modern English; the compound 'algae-controlling' is a contemporary adjectival formation combining these elements.

Individually, 'alga' originally referred to 'seaweed' and 'control' meant 'to check or regulate'; combined in modern usage they form a descriptive compound meaning 'capable of regulating or suppressing algae growth'.