My question is the same as Sponner's. I've read through the discussion and can't find an answer, As for Atdabom's comment as to English grammar my advice is - Forget English Grammar. You are learning Spanish and Spanish grammar. You'e gotten this far and are still clinging to English grammar. Way back in Lesson One we learned that "nouns are masculine or feminine" and "verb endings change to describe who and when" and "adjectives change with the gender and number of the noun". In ingles (no capital letter) an apple is an apple. It's neither male nor female. Es espanol. No accents (another big difference between ingles and espanol)) in the comments section.
Because tanto mean "so much". Tan on its own means "so". Someone put it like this above. Use tan with adjectives eg I am AS good AS you but tanto(a) with nouns - I have AS MUCH money AS you. And if you can count the things use tantos (as) eg I have AS MANY cars as you. In this question it is even more general, not money or cars just AS MUCH so use tanto on its own without any noun. In every case the second AS is "como".
Because Spanish is more insistent on correct grammar. If it was the other way round i.e. "Tienes tanto como yo" the strictly grammatically correct translation would be "You have as much as I" (because it is said you are really saying "as much as I have" so it can't be "me" can it?) However, it sounds in English, speech at least, too stilted and usually "as much as me" is said. But as I said, tjhe Spanish are not so lax and hence "tú" above and "yo" in my example. Does that help?
Tú - You (singular, informal version)
Tu - Your (singular, informal)
However, in Spanish, since verbs in Spanish conjugate to match their corresponding pronouns, Spanish speakers will usually omit "tú" when referring to their listener. The only time you will want to add the pronouns is when you want to avoid ambiguity or to add emphasis.
I'm pretty sure the phrase "tant(o) como" is a comparative phrase that together means "as much as".
The two words apart mean different things.
If you have never been formally taught a unit in Spanish about Comparatives & Superlatives (or you've just forgotten the concepts), I'd recommend googling the topic.