HELP pH Lows

[artista]

I recently purchased a pH meter and my readings I am getting are pretty scary. I bought all the fluids and checked calibration so I am led to believe that these readings are correct. First off, my tank and all the living creatures from starfish to fish and corals all are happy and active. The corraline is taking over everything and the corals are open and growing. I am still fighting the hair algae but it is receding. I have been very busy with my new sign business and traveling in and out of town this summer and have been watching my corals for any signs of stress instead of testing. I know this is not always accurate but my corals have always been the first to tell me if anything is "not quite right".
A little background My tank is a 125 gallon with 55 gallon sump/refugium. Lights are on 10 hours in the daytime (5 hours MH) and refugium lights 24/7. The tank was a neglected 4 year old tank when I purchased it. I have had it running since November. All readings were within normal range from January through May. Phosphates/nitrates were high (now using RO/DI water). Have had a hair Algae problem due to well water. Did 5 major 35-50 gallon water changes in May-June to help rid the system of hair algae.
My tank pH is reading 7.70 in the daytime and can go as low as 7.58 at night. My RO/DI water pH reading is 6.1 and after mixing in instant ocean and aerating with 2 powerheads and an airpump for a week, the pH of my waterchange saltwater is only 7.58. I have been adding straight RO/DI for about 2 months and dripping Kalk 1-2 times a week.
Are my readings so low because I am adding such a low pH freshwater to the tank? Why would my makeup water be so low in pH? I thought that instant ocean was supposed to level the pH? I know that 4 months ago I wasn't having this problem with the tankwater although I don't have any readings on the makeup saltwater.
Any constructive comments or help would be appreciated. I am a little lost with these results and need to get this headed in the right direction ASAP.:notsure:

 

[blitt]

have you used a ph buffer I use seachem "ph 8.3 Marine Buffer" It works really well

 

[sebae0]

where is all the equipment located? is it in a closed room with little air flow? sometimes a room with little fresh air flow can build up co2 in that room and make getting your ph high enough where you want it. the levels are not high enough to harm you but affect the water. i nevere beleive this either until i put an in wall tank in my basement.

 

[artista]

Actually, I have looked into this and am leaving the window next to the tank wide open at night and cracked in the 90-100 degree daytime. Doesn't seem to be helping.

 

[sebae0]

do you have tops on the tank? any powerheads pointed at the water surface to help move the top of the water? and are your calcium, and alk levels in check?

 

[kpk]

Read up on dripping kalkwasser 24/7. It will bring your ph up, but be sure to monitor. Look up dripping kalkwasser 101 by kip. There is tons of info. there and that could help.

 

[kpk]

didn't realize this was 2 months ago