PH Problem on New Tank
 

I set up a 40 gallon tank on Sunday with 50 pounds of Southdown Play sand
and 50 pounds of Fiji live rock, using RO/DI water and Instant Ocean Salt.
On Sunday after setting my tank up my PH was 8.1 and my salinity was 1.026.
I checked my PH today and it is 7.6 and salinity 1.026. I cannot figure out
why my ph is dropping. I have had a 75 gallon tank for several years and
have redone it several times and have never had this problem. Any
suggestions? Some locals stores have told me this is a cycling issue, this
does not sound right to me.

Thanks
Travis