librarygirl
Look It Up
I agree with JLK for what it's worth; PH at 6 is going to stop the nitrification process. WIthout fish in the tank there's no worries about fluctuations right now, just get it higher. IF it keeps dropping, adding some crushed coral or argonite to the filter will help keep the PH stable; my water is very soft and I have some CC in my filter to keep it stable. IT's sold at most pet/fsih stores in the saltwater section (unfortunately it comes in large bags and you won't need much). Here's some info on PH and nitrification:
pH
pH
The optimum pH range for Nitrosomonas is between 7.8-8.0.
The optimum pH range for Nitrobacter is between 7.3-7.5
Nitrobacter will grow more slowly at the high pH levels typical of marine aquaria and preferred by African Rift Lake Cichlids. Initial high nitrite concentrations may exist. At pH levels below 7.0, Nitrosomonas will grow more slowly and increases in ammonia may become evident. Nitrosomonas growth is inhibited at a pH of 6.5. All nitrification is inhibited if the pH drops to 6.0 or less. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+ state
From Nitrifying Bacteria Facts
The optimum pH range for Nitrobacter is between 7.3-7.5
Nitrobacter will grow more slowly at the high pH levels typical of marine aquaria and preferred by African Rift Lake Cichlids. Initial high nitrite concentrations may exist. At pH levels below 7.0, Nitrosomonas will grow more slowly and increases in ammonia may become evident. Nitrosomonas growth is inhibited at a pH of 6.5. All nitrification is inhibited if the pH drops to 6.0 or less. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+ state
From Nitrifying Bacteria Facts