[MarkoD]

I can't help but face palm myself after seeing what some people are posting.

Here's a quick tutorial:

You're- means "you are" (you're stupid for not knowing this)
Your- refers to something that belongs to the person you're talking too(your reef tank)

Their- when something belongs to someone (their reef tank)
There- referring to a place (look over there)
They're- means "they are" (they're really nice people)

We're- means "we are" (we're really nice people)
Were- past tense of "to be" (they were just here)

This is a period. It allows the reader to know when one sentence finishes and when the next is about to begin