You have been given some good advice there.....
One of the reasons that I don't upgrade is the availability of getting some corals here where I live. We do have alot of anemone's come into our LFS here but no one in my opinion in these stores has any idea what they are doing with them. They will sell you just about anything.
I started out with 3 single mushrooms: green, red, green hairy. These have mulitplied in my tank quite nicely. I just as a matter of fact scooped up one green hairy and one green mushroom and placed them on other areas of the tank I would like more mushrooms to grow. To get a nice clump of mushrooms here I am talking about 6 in a cluster we pay $55.00 CDN..... :scared: Yep you hear right, all our corals are shipped in and we pay dearly for them. Single mushrooms $9.00 CDN but I have found a nice place 30 min from my home town that has some nice singles for $5.00 CDN I will be paying them a visit...
So if you plan on going into anemone's etc I highly recommend that you upgrade your lights like suggested, this will give you the best choices of corals for your tank. If you are like me where selection is very limited then the light I have will be just fine.
You asked where I found the 18,000k. The light that came with my system is your everyday warm florescent light. I bought a Coralife Power Glo 20 watt 18,000k from my LFS. It says right on the bulb and packaging it comes in as to what the watts are the the kelvin rating.
Good luck to you, make sure you do it right the first time to save yourself money in the end.