Live rock colour variations within a reef tank
 

Still a relative newbie at this having setup my 150 gallon tank about 11 months ago. Have recently seen a noticeable change in the tank as some of the live rock has turned a darkish/gray colour, while some is still purple, violet, green and various others with a dozen or more poly's popping up from time to time. Question, should I be concerned re: the darker colour on some of the rock as per pics attached? Have also had some black growths on a few of the rocks that may show up on the pics.

I have recently changed the white lights to 54w 10,000K T5 HO's and tests are in the mid-range. Anyway, any thoughts are appreciated.

I was concerned about black growths on my rocks once as well but it turns out it was some type of sponge/coral. Are they soft but firm to the touch and rounded? I'm not sure about your live rock issue, I had a bunch bleach out on me when I put MH bulbs over them but they turned purple again after awhile. Are calcium/alk levels OK? Too long of a photoperiod or a change in lighting can change the coloring for awhile. If everything else in the tank is doing well and levels are OK all I can say is keep up with water changes and I'm sure the color will come back, sometimes very slowly.

Coralline can die if you don't keep up on calcium and alkalinity, or you don't do enough water changes.

alot of times that the 6500K and 10k can actually bleach out your rock and the coraline too . I ran into the same problem but doing water changes isnt actually going to bring your coraline back to life.. well may be the cal and alk will keep up but itws the PH that is being stable is causing your coraline to grow.
if you notice that flouresant bulbs are the best for growing coraline algae. like VHO's or Normal flouresants.

but be careful what you wish for kido. Once the coraline starts growing its going to start consuming yuour CAL and ALK. trust me my stank can easy suck up the CAL and ALk in my SPS tank if I ckeep the coraline off the sides it slows it down so much that my Kalk reactor can handle it /

I was suggesting water changes to help keep the calcium and alkalinity at a decent level which should help the coralline growth.

Mindy i wasnt saying that you were wrong im just stating that proper PH levels will keep the coraline at a normal rate.
but yes cal and alk has a huge part in there too. may be i just worded it wrong sorry about that .

I was clarifying what I meant for the OP, I wasn't sure I was clear when you made that comment after. :lol: You're right though, a low pH does tend to limit coralline.