Swim in the Ocean

I wrote 231 entries in the past three years, and my language exchange partners on Lang-8 corrected my entries, but yet I can't write any entry without a mistake.

I learned English grammar in school, and to some extent I understand it, but to read a book about swimming and to swim in the ocean actually are much different.

Elements, which we don't have in Japanese language, are especially difficult for me, for example, the usages of "a" and "the" or singular and plural, the pronunciations "r" and "l".

Of course I know that I should add "s" to a noun, when the number of it is more than 2. But sometimes I encounter the case that I can't distinguish if a noun is singular or plural.

I wrote, "I can't write any entry without a mistake."

I have found both of the expressions, "any one" and "any ones," so I wonder which is correct between "any entry" or "any entries." And at the end of this sentence should I write "without a mistake" or "without mistakes" or "without any mistake" or "without any mistakes?"

Although I also know the anatomically positions of tongue in a cavity of mouth at the pronunciations of "r" and "l", I can't pronounce and distinguish "r" and "l," and I often make a typo of "r" and "l."

On Lang-8 one of my friends made a correction about the usage "a" and "the", but another friend wrote that my sentence was right. And then they stared a long discussion about definite article and indefinite article.

When I read this discussion, I was a little relieved because I realized that sometimes it was difficult even for a native speaker to swim actually in the ocean.