PH issues

[p1u5h13r4m24]

I have recently upgrade my tank from a 60g to 120g system. When I had a 60g my ph never dropped below 8.0 even at night. Now with the 120 I’m dropping to 7.65 at night and 8.1 max during the day. This is not a probe issue I test with 2 probes and I’ve checked them with solution they are accurate. I use kalkwasser in my ato. I have a line ran outside connected to my skimmer. I have a c02 monitor in my house when windows are open it’s around 420 ppm with them closed it averages 6-700ppm. I’ve read that even 8-1000ppm I should still have 8.0 ph. I notice when I feed a bit less I have a little better ph but I’m already only feeding about 1 cube a day. I’m lost I’m not sure what to do but I’ve lost about 2-3k in sps so far. Any ideas would be great

 

[jsker]

Where is your tank located?
Are you using the same skimmer?

 

[ScottB]

I crank my kalk stirrer pretty hard to keep pH up over night. Four liters into a 300G system. My ATO rarely needs to kick on. I can finally open the windows and that helps a ton.