I use emerald themes with KWin via Smaragd. However, it seems whenever I open or close a window, KWin's ram usage keeps increasing by 1 MB for every window opened. Would anyone know of a fix for this memory leak? Or... perhaps an alternative to the plugin that KWin could use to apply Emerald themes?

Emerald and Smaragd colour themes are third-party colour schemes, you need to report this to the authors of your theme.