Chronic pH issues

[ReeferDave01]

Reefers, I have a chronic pH issue. It varies 7.75-7.85 and I can’t seem to get it above 8.0 unless I put buffers in the tank. I have Reef Octopus Skimmer & have bought BRS CO2 scrubber & attached it to skimmer. I replace CO2 media every couple of weeks or so. I was able to bump pH to 7.8 with scrubber (before it was even lower). I'm running Phosguard & have 2 refugiums that run 16 hrs day counter cycle to tank (1 in sump & 1 hang on attached to my small 60 gallon). I'm also dosing Kalk every hour 50 ml of 1.5 teaspoons/gallon Kalk mixture. Running air line outside or opening door is not an option. The main tank has glass top. I've tried opening it, made no difference. I live in Phoenix so I have chiller, heaters, T5s (run 2 hrs day) & LED (run 10 hrs day). I even bought a CO2 monitor (for inside house) and it reads 600-900 ppm for most part (which is normal). I have ~25 fish & ~20 corals between 2 tanks. Feed them 4 cubes a day. When I travel, I run Apex auto feeder 3x a day. Have 3 socks I change 2-3x a week. I have auto water exchange about 1-2 gallons/day + ATO, and do additional 20 gallon change once a month. I have 4 powerheads including Maxspect Gyre so there is plenty of water circulation in the tank.

Any suggestions how to increase pH would be appreciated.

My Parameters:

Total tank volume – 350 gallons (main tank 210, small tank 60 & sump 80)
Alkalinity - 11.2 (Hanna)
Ammonia – 0 (API)
Calcium – 545 (Hanna) – always been 500-540
Magnesium – 1440 (Salifert)
Nitrate & Nitrite – 0 (API)
Oxygen – 8 (Salifert)
Phosphate – 0.25 (Salifert) & 0.33 (Hanna ULR)
Temp – 78-78.5 (Apex)
Salt – 34.9-35.1 (Apex)
ORP – 340-360 (Apex)

 

[JamesP]

Have you done the bubble test? Bubble a cup of tank water outside for an hour with an airstone. Come back in and test the ph of that cup right away. I would bet it will be way higher. Now get a new cup of tank water and do the same test while indoors. If the ph went up from the outside test, you still have a co2 issue. If it went up from the second test done indoors you have the issue because of bad gas exchange. If it does not go up in the second test you have high indoor co2.

 

[ReeferDave01]

Well now Im completely stumped. Just did the experiment. I did 2 cups with bubblers, one indoor & one outdoor. After an hour. I took reading with handheld:
Aquarium - 7.79 (Apex reading was 7.82)
Indoor water cup - 7.76
Outdoor water cup - 7.64 (I took this reading 3x, each time rinsing probe off with RODI)

 

[hermitmandy]

I'll have to try this on my own tank, as I'm having a similar issue.

Edit-quote failed. Meant to quote bubble test post.

 

[JamesP]

At a dkh of 11 your ph should be at 8.4 with normal co2 levels. Thats strange. Im going by one of Randy Holmes Farley's articles.

http://www.reefkeeping.com/issues/2004-09/rhf/

 

[LostInTheDark]

Have you tried re-calibrating the probes? Maybe try a different way to measure just to double check. Salifert PH is ony 10 bucks and would confirm your readings.

 

[Reef 450]