when i cycled my live rock from liverocks.com my tank did the same thing. it when away after the cycle was done. but a ph
did help some. but i think the reason it was there is because i did not have a skimmer on the tank during the cycle.
A 46 gal
bow front (Soft coral) reef tank with a 10 gal
sump. And a 30 gal
and Clam) reef tank hooked up to the sump of the 46 so they share water.