I like 15K, still gives you good colour and the growth is decent

Any discussion of colour and growth potential with respect MH bulbs in purely general terms is pointless without reference to Sanjay Joshi's testing:

http://www.reeflightinginfo.arvixe.com/

Choose your ballast, choose your bulb and off you go. PPFD (a.k.a PAR) and CCT (a.k.a. colour) are the most important columns. Actual power consumption in term of watts is useful as well.

Of course colour preference is purely subjective and mixing in supplemental lighting such as actinics adds to the choices you have.

Having supplemental actinics gives you more flexibility since you can use a bulb with higher PAR which are GENERALLY in the lower-K more yellow range.

i get good growth out of my 15k's but the colors especially pop-put when the bulbs are newer

Mark I got them at Hidden Reef in Abbotsford, they are actinics but a bit different blue, nice light.

Doug