Learn Hardcore Japanese: watasi ga setumeisitara, gokai ha sugu kieta. - When I explained, the misunderstanding quickly disappeared.

Inside subordinate clauses (like the 〜たら clause), Japanese normally marks the clause-internal subject with が, not は. Using は there would try to topicalize across the boundary and sounds unnatural. So 私が説明したら is the natural choice. It can also imply slight contrast or emphasis on “I (not someone else).”

Why is 誤解 marked with は? Could I use が instead?

Both work, with nuance differences:

誤解はすぐ消えた: treats the misunderstanding as the topic (already known in context), focusing on what happened to it; can feel slightly contrastive.
誤解がすぐ消えた: presents “the misunderstanding disappeared” as new, event-focused information. Your original feels like “As for the misunderstanding, it disappeared right away.”

Can I say 誤解を消した instead of 誤解はすぐ消えた?

Not idiomatic. 消える is intransitive (“disappear”), while 消す is transitive (“erase/turn off”). For misunderstandings, the natural collocations are:

Intransitive: 誤解が解けた (“the misunderstanding was cleared up”)
Transitive: 誤解を解く / 誤解を解消する (“to clear up a misunderstanding”) 誤解が消えた is understandable but less idiomatic than 誤解が解けた.

Does 〜たら here mean “if” or “when/after”?

Here it means “when/after.” With a past main clause (…消えた), 〜たら almost always reads as “after X happened, Y happened.” If the second clause were non-past, it could be conditional:

私が説明したら、誤解はすぐ消えた = after I explained, it disappeared.
私が説明したら、誤解はすぐ消える = if/when I explain, it will disappear.

How do 〜たら, 〜ば, and 〜と differ in this context?

〜たら: flexible; often “when/after” for one-time events, also used for conditions. Best for sequential, past narratives.
〜ば: more hypothetical/general; good for rules or tendencies. One-time past result feels odd: 説明すれば、誤解はすぐ消えた sounds off.
〜と: automatic/immediate result or “and then.” In narratives, can mark a discovery: 説明すると、誤解はすぐ消えた is possible, with a “the moment I explained, then…” feel.

Could I say 説明すると、誤解はすぐ消えた?

Yes, especially in narrative style. 〜と here suggests an immediate, almost automatic follow-up: “I explained and then (right away) the misunderstanding disappeared.” 〜たら is the safer, more neutral choice for everyday narration.

What about 説明したところ?

Vたところ means “when I did V, (I found that) …,” highlighting the result at that point. It’s a bit more formal and pairs well with polite forms:
ご説明いたしましたところ、誤解はすぐ解けました。

Does すぐ need に? What’s the difference between すぐ and すぐに?

Both are correct and mean “immediately.” すぐに is a touch more explicit/formal. Variants:

すぐさま: emphatic “at once” (spoken, somewhat dramatic)
直ちに: very formal/official “immediately”

Can I omit 私が?

Yes. Japanese often drops obvious subjects:
説明したら、誤解はすぐ消えた。
Keep 私が if you want contrast/emphasis (“It was when I explained (not someone else)…”).

Is the comma after 説明したら required?

No, it’s optional. It just aids readability. Both are fine:
私が説明したら、誤解はすぐ消えた。 / 私が説明したら誤解はすぐ消えた。

Are spaces normal in Japanese writing?

No. Standard Japanese doesn’t insert spaces between words. A conventional version is:
私が説明したら、誤解はすぐ消えた。

How do I read the sentence?

Watashi ga setsumei shitara, gokai wa sugu kieta.
Kana: わたしがせつめいしたら、ごかいはすぐきえた。

Can I say 説明をしたら instead of 説明したら?

Yes, but 説明したら is leaner and more common in everyday speech. 説明をしたら can sound heavier/more formal. In business politeness you’ll see things like ご説明いたしましたところ、… more often.

Could I mix tenses like 説明したら、誤解はすぐ消える?

You can, but it changes the meaning to a conditional/general tendency: “If/when I explain, the misunderstanding (typically) disappears.” For a one-time past event, keep both clauses in past: …消えた.

If I want to show clear causation (“because I explained”), what should I use?

Use an explicit reason connector:

私が説明したので、誤解はすぐ解けた。
Or instrumental: 私の説明で誤解はすぐ解けた。 (by means of my explanation)

Is 消えた the best verb here, or is there a more natural choice?

It’s understandable, but the idiomatic choice is usually 解ける for misunderstandings:

誤解はすぐ解けた。
Transitive alternatives (if you’re the one clearing it up):
誤解をすぐ解いた。 / 誤解をすぐ解消した。