For this question:
"El guiso solo necesita una pizca de sal. No pongas ____ "
I couldn't decide whether it should be "tantas" or "tanta" because it wasn't clear to me at all whether the pronoun is referring to "una pizca" or "sal". If I recall correctly I put "tantas", attempting to agree with "una pizca" but it was the wrong answer. Is it possible that both might be acceptable in real world speech because of that ambiguity, or am I missing some clear difference?
(e.g. in English "This stew only needs one pinch of salt. Don't put too many" would sound a bit wrong, but technically would be correct for the same reason, in my opinion. Of course you'd usually hear "This stew only needs *a* pinch of salt. Don't put too much.". While salt is an uncountable noun (in most contexts), "pinch" is, of course, not!)