Question

any advice on the best way to use when to use tan vs. tonto?

Answer 1

You mean "tan" vs. "tanto"?

I mean this is a really good question. I don't think my teachers ever taught us this, in class.

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TAN usually means...
"So"
"As"

Example:

"Tu pelo es TAN largo."
"Your hair is SO long."

"Pedro es TAN alto como Isabela."
"Pedro is AS tall as Isabela."

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On the other hand, TANTO usually means...
"So much"
"So many"
"As much"
"As many"

Example:

(And I quote Shakira)

"Aye, amor me duele TANTO."
"Oh, love hurts me SO MUCH."

"Yo tengo TANTO dinero como Pedro."
"I have AS MUCH money as Pedro."

Answer 2

It's a funny typo because "tonto" means "stupid". Be careful when you say it!