Need Advice RE: pH/CO2

[Hooloovoo]

I have had my tank setup since early October, and I am fairly happy with my water parameters, except for pH, which keeps creeping too low for my liking. The tank is in my 10x10 office, so I suspect the problem is the build up of CO2. To mitigate this, I have been keeping the doors to the office open as much as possible and the ceiling fan going to pull in air from the rest of the house while I have the patio doors open to bring in fresh air. Still, it's a struggle to keep pH from falling below 7.8.

I am using Red Sea Reef Crystals for my salt, and this seems to be keeping my Ca and Mg sky high since I have not added any corals or other Ca consuming critters yet due to my concerns about the pH. In fact, I am seeing the buildup of some white residue around my powerheads and overflow, which I suspect may be precipitate from excessive Ca.

I am wondering if there is something more I can or should do to keep my pH up at a better level for coral health?

Further details:

DT: 20 Gallons
Sump: 10 Gallons
Refugium: Chaeto w/ lights set to run on schedule opposite to DT lights
Circulation: 2x 240 gph Hydor Koralia Powerheads + Sicce Synchra 0.5 return pump
Skimmer: Hydor Slim Skim Nano
Current Parameters:

Salinity: 35 ppt (JBJ Refractometer)
Temp: 78 F
pH: 7.8 (API)
Ca: 523 ppm (Hanna Colorimeter)
Mg: 1480 ppm (Red Sea)
Alkalinity: 8.4 (Hanna Colorimeter)
Phosphate: 0 ppm (Hanna Colorimeter)
Ammonia: <0.25 ppm (Salifert)
Nitrite: <0.1 ppm (Salifert)
Nitrate: <0.2 ppm (Salifert)

Current Inabitants:

CUC (Nerites, Ceriths, and Nassarius)
Yasha Goby
Peppermint Pistol Shrimp
Juvenile Ocellaris Clown (2)
Green BTA (Sm.)

[Scubajoe1]

What are you using for your Ca and Alkalinity dosing? I had the same issue and wanted my pH a little higher. Instead of BRS 2 part I now dose with Kalkwasser and my pH hits 8.3 in the day and 8.0 at night. Still may add some CaCl2 depending how much my corals use.

[mindi]

I use Randy recipe 1( version 2) and it works perfectly, is easily adjusted up and down, and is so cheap that you can regard it as free. Works perfectly and to be honest I cant think of a reason to actually pay for a 2 part commercial solution with money that would buy a nice coral. I have been using these recipes now in two tanks of 100 and 150 gal for several years and am certainly not changing. The beauty of them is that even if you dont weight the dries super accurately you auto correct when you measure and adjust the doing volumes....ie if you make your Calcium ( Pool Water Hardener + RO) a little weak you adjust the error out in the dosing setting....If you do weigh the dries accurately then you just dose equal amounts.

http://www.reefkeeping.com/issues/2006-02/rhf/