Hmm... either that post was edited, or I was blind as a bat!
OK - first thing... water doesn't "cycle" for a year and a half. Cycles
seem to last forever, but not that long!
Did you mean your tank has been set up for a year and a half?
How big is the tank and did you just recently add any of those fish? A sudden increase in bioload (adding more than one fish at a time) could've caused a little spike in ammonia while the beneficial bacteria play catch up and increase their population.
pH will normally drop during a cycle due to all the biological activity going on in a tank, so I'd guess that for whatever reason, you're seeing a mini cycle. When the cycle is over, and after water changes, the pH will normally go back up to where it should be.
{Edit: Looking over your previous posts, looks like this is the 56g tank? And also, sounds like you were thinking about adding more live rock, as mentioned here...
http://www.aquariumadvice.com/forums/f11/live-rock-108111.html . Did you end up adding any rock? If you did, and it wasn't fully cured, that could be the source of your ammonia and the mini cycle. Adding uncured live rock to an existing tank will often cause another cycle due to the stuff on the rock dieing off.}