New to supplement/doseing

[pirate]

So I'm starting to think I should be dosing a reef supplement. I don't dose now and am looking at what I should start with, and what I should be testing for. Can I use a all in one type? Or is it better to use single ones and add what is needed? And if single ones what ones should I start off with first?
The reason I'm thinking this is my softies are doing quite well, but my sps and lps don't do anything. My tank is 150g (5x2x2) wih 2x250w hqi at either end as well as 2x65w pc artincs, over the top of the tank. I do a 5g water change at a time, I'm not set up to do a large one.
So what should I start wih first?
Thanks

[cuz]

Start with testing to see what if anything your tank might be lacking..

[e46er]

http://reefkeeping.com/issues/2006-02/rhf/index.php
Read this
Don't dose anything your not testing for
Get setup for larger water changes 5 gal in a 150g system does nothing

[Money pit]

Another RHF link. For the various perimeters
http://reefkeeping.com/issues/2004-05/rhf/index.php