Yes higher. When it goes below 7.0 & approaches 6 things slow down. Someone much smarter than me explained that the nitrifiers that convert ammonia to nitrite use up calcium carbonate in the process which lowers the pH. I had this happen to me when I was cycling some 40 breeder tanks. All of a sudden everything came to a screaming halt, Ammonia levels started appearing and there was no nitrite production. My pH was 6.0. I added some Seachem Alakaline buffer and brought the pH back to 7.4 and bam the ammonia was converted to nitrite within 24 hours and the cycling progressed. Now when cycling tanks I monitor my pH. My tap water only has a kH of 3 degrees so I carefully monitor pH more closely. Once tanks are fully cycled my pH stabilizes at 7.6. But during the cycling process it is subject to some wild swings due to my lower kH which helps stabilize pH.