Combining multiple symmetric encryption algorithms - implications? I was just wondering if I add more security by combining two or more symmetric encryption algorithms on a plain text. 

For example: Plaintext → AES → Twofish → Serpent

Of course a different key and IV (produced with a cryptographic secure prng) is used for each algorithm. Speed fortunately is not important.

Or does this form of combination has other implications I do not see?

There is a question like that here at Crypto.SE (Is TrueCrypt&#39;s multiple/cascading encryption safe?) but it focuses on using the same key.
I can see based upon your question that you're not already a crypto-expert.  Given that, I think the single most useful answer I can give you is this:


  Multiple encryption addresses a problem that mostly doesn't exist. Modern ciphers rarely get broken -- at least, not in the Swordfish sense. You're far more likely to get hit by malware or an implementation bug than you are to suffer from a catastrophic attack on AES.


That's a quote from http://blog.cryptographyengineering.com/2012/02/multiple-encryption.html, which is an excellent article on this topic.

Moreover, if you have to ask this question, you should not be using multiple encryption.  It's a little bit tricky, and you're more likely to screw something up than to get any meaningful security gain.

Bottom line: No, you can't add more security by using multiple encryption.  The block cipher isn't the weak link, and strengthening the strongest link in a system does not add more security.  Modern block ciphers appear to be effectively unbreakable; if that's correct, multiple encryption is pointless.  So, my recommendation is: don't do it.  It doesn't solve any real-world problem, it doesn't add much benefit, and it adds the extra risk that you might screw something up.  Use standard well-vetted cryptographic solutions, like TLS, Truecrypt, GPG, etc.