I use a pseudonym everywhere. Literally, everywhere. You cannot find me online using my real name, but if you know what pseudonym I have, then you can find out a lot about me (not personally of course, but things like forums posts, and such).
It sounds like your pseudonym was originally created, and is still mostly used, as a kind of internet identity. That being said, I would recommend you keep it to that, and not put it on your CV, or use it to represent your real-life self.
I even use this pseudonym as my LinkedIn name. I'm also filling in this name every time some field asks me for my "Real Name".
For websites that involve demonstrating yourself in a professional manner, or anything "official", you should use the same name that you go by in real life; the one you answer to all the time, to everyone, always. This should also be the same name that you put on your CV.
For a CV, I would use my real name and put my pseudonym in quotes, is that enough?
For a CV, if you were using a pseudonym in real life, then you would put that and nothing else. You should not include both your pseudonym and real name; it defeats the whole purpose. Legally speaking, the only time that you are required to disclose your true name to your employer is when filing out paperwork with HR. At that point, you would provide both your pseudonym and real name. If anyone else is to know your real name, it's completely at your discretion.
So, my question is, is this see as unethical and would hurt my professional "image" if an employee/colleague finds out that I'm using this fake name, even if I shouldn't?
It depends on why you're using the pseudonym.
When people use pseudonyms in real life, there's generally a reason why. For some people, it's because of various legal issues; for others, perhaps they're in the process of getting their name changed, and are going by the name preemptively. Also, it could be that someone has a high exposure job, and wants to keep family and work as separated as possible. That being said, if someone finds out you're going by a pseudonym, you'll probably have to provide some kind of explanation. If not, it will become extremely tense between the two of you, and word may spread to other employees/colleagues. To be on the safe side, only go by a pseudonym if your reason why is sensible & justified; i.e., if you really need to.
..it's obviously not a real name - it's basically two conventional words from the dictionary..
If even you don't think it sounds like a real name, should you really be using it to represent yourself on a professional social networking site, or putting it on your CV? Hmm, I would think not..
I'm sure your real name is just fine, and recommend you stick with that when in a professional setting.