[QUOTE=Poseidon;145055]pH is dramatically affected by atmospheric CO2. Have you had your windows open/closed?
You are correct about alkalinity having an effect on pH as well, it is the buffer that must be controlled to keep you pH consistent.
Also, with no "life" in the tank, you should not have much of a pH swing yet. Coral and macro algae do go through a respiration cycle, day and night. Once you have a tank and sump going, you can set your sump to be lit opposite of the tank, which will also help stabilize pH swings.
There are a lot of products on the market that claim to help with pH, in my experience the best was an Aqua Vitro product called.... but I can't recall it at the moment, "Stabil" maybe. It is hydroxide ions in solution. However, you are not to the point of needing to add ANYTHING other then time right now.
[COLOR="Silver"] ---------- Post added at 08:47 PM ---------- Previous post was at 08:46 PM ----------
Well put.the 7.8 will rise but starting a reverse light cycle on the fuge
will help keep consitant buffer capabilities. I personally never used the shrimp to cycle a tank.just time and patience but have read of allot of other reefers doing it.Raiseing ammonia is something I never intentionally did.No 2 ,Po4 ,Alk,Ca and No3 levels are usually what I concern myself with once the ammonia reaches 0.