Если киви слишком кислый, я кладу в смузи больше манго.

Because Если киви слишком кислый is a subordinate clause introduced by если (if). In Russian, an если-clause is separated from the main clause by a comma.

So the structure is:

• Если ... , я ... = If ..., I ...

You would also use a comma if the order were reversed:

• Я кладу в смузи больше манго, если киви слишком кислый.

This is a very common question because киви is an indeclinable loanword, so its form does not change, and its grammatical gender can feel unclear.

In this sentence, киви is being treated as masculine, so the adjective is masculine too:

• кислый = masculine singular

In real usage, with indeclinable nouns like киви, you may sometimes see variation. For the fruit, masculine is very common in everyday speech, so кислый киви sounds natural to many speakers.

The main point: the adjective must agree with the gender the speaker is assigning to киви.

Кладу is from класть, an imperfective verb. Here it describes a habitual or repeated action:

• Если киви слишком кислый, я кладу в смузи больше манго.
• If the kiwi is too sour, I add/put more mango into the smoothie.

This means something like whenever that happens, that is what I do.

Положу is perfective and usually refers to a single completed future action:

• Если киви слишком кислый, я положу больше манго.
• If the kiwi is too sour, I’ll put in more mango.

So:

• кладу = habitual / general rule
• положу = one specific future action

Both can work.

• кладу literally means I put
• добавляю means I add

With food ingredients, Russian very often uses класть in places where English would naturally say add:

• кладу сахар в чай
• кладу ягоды в кашу
• кладу манго в смузи

So кладу is natural.

That said, добавляю is also very natural here and may sound slightly more explicitly like add:

• Если киви слишком кислый, я добавляю в смузи больше манго.

Normally, в can take different cases:

• в
  • accusative for motion into something
• в
  • prepositional for location in something

Here, with кладу, the meaning is motion into the smoothie, so grammatically this is в + accusative.

But смузи is indeclinable, so its form does not change. That is why you still see:

• в смузи

Even though the case is accusative here, the word looks the same.

After больше (more), Russian normally uses the genitive:

• больше сахара
• больше воды
• больше времени

So in this sentence, манго is grammatically in the genitive after больше.

However, манго is also an indeclinable noun, so its form stays the same:

• nominative: манго
• genitive: манго

So больше манго means more mango, even though the word itself does not visibly change.

Yes. That is completely possible.

Russian often allows то in the main clause after если:

• Если ..., то ...

In this sentence, то is optional.

So both are natural:

• Если киви слишком кислый, я кладу в смузи больше манго.
• Если киви слишком кислый, то я кладу в смузи больше манго.

Adding то can make the sentence feel a little more clearly structured, but it is not required.

This is an important meaning difference:

• очень кислый = very sour
• слишком кислый = too sour

Слишком means the sourness is excessive or undesirable. That fits the second part of the sentence, because the speaker reacts by adding more mango.

So the logic is:

• kiwi is too sour
• therefore I balance it by adding more mango

If you said очень кислый, you would only be describing a strong taste, not necessarily a problem.

Yes, often you can.

Russian frequently leaves out subject pronouns when the verb form already shows who the subject is. Кладу already means I put.

So this is also possible:

• Если киви слишком кислый, кладу в смузи больше манго.

That said, keeping я is also perfectly natural. It can make the sentence a bit clearer, a bit more explicit, or a bit more contrastive depending on context.

Not necessarily. In Russian, the present tense is often used for habitual actions or general rules.

So here я кладу means something like:

• I put
• I usually put
• I tend to put

The sentence is not just about what the speaker is doing right now. It describes a normal response whenever the kiwi is too sour.

Yes. Russian word order is flexible, and changing it changes emphasis more than basic meaning.

The given sentence:

• Если киви слишком кислый, я кладу в смузи больше манго.

is very natural.

But you could also hear:

• Если киви слишком кислый, я больше манго кладу в смузи.
• Если киви слишком кислый, я кладу больше манго в смузи.

These all mean roughly the same thing, but the focus shifts slightly:

• в смузи earlier can emphasize where it goes
• больше манго earlier can emphasize the amount/ingredient

For learners, the original version is a good neutral model to follow.