I just hit level seven where you start having this problem. Everyplace I read says that post war there is phonetically zero difference. Is there a trick to remembering the correct form of these that anyone uses? It almost seems like it would only reallllly matter if I wanted to take jlpt or something.
Haven’t even had the words long enough to fail a review on this technicality yet, but I for sure see it coming and already find it making the words themselves more cumbersome to remember because I feel like I’m mentally focusing more on this than the actual kanji/reading/meaning pairing. (and trying to remember that I type it “di/du” makes me almost go to remembering it phonetically with the d sound).
Almost always the characters ず and じ are used. The few exceptions are primarily because of rendaku, i.e. a word like blood・ち・血 is in the word nosebleed・はなぢ・鼻血. If you know the original word is ち then that can help you remember the correct spelling in “nosebleed.”
In general, ぢ is so rare, it tends to stand out when you actually have to use it.
づ is slightly more common, but still pretty rare and I’m guessing it’ll pretty naturally stand out to you in another month.