ph 7.85 night and 8.1 day???

[sanababit]

hello guys, im running a 46 gal tank with a reefkeeper 2 controller, anyways the controller has a ph probe hooked up and calibrated, i tested the reading on the RK2 and a regular ph tester i have and they are off by .06 ph, the problem is that at night i get a reading of 7.85 +-.06 lets say for goodnees sake its at 7.91, and at day i get 8.1 +-.06 lets say 8.16, question , is this a good range of ph to work with or whats going on, param on tank are

ph 7.91 night and 8.15 day
amm 0
trite 0
trate 20
temp night 78.9 day 81.7
phos 0
ca 440
alk 7 dkh
mag dont have a tester

btw if i test my ph with an API tester it always comes out about 8.3, since its a color chart its always in between colors, i test in the afternoon always. how can i control ph better?????, and before anyone asks i do have a refugium running with a 75watt light running 24/7, shouldnt this stabilize ph????

sana

[bertoni]

That range isn't that bad. I wouldn't worry too much. A lime drip might help with the pH. The 75 W bulb is likely not enough to drive photosynthesis rates enough to keep the pH higher, although something else (nutrients, space) might be the limiting factor.

[Ebisan]

My pH range is exactly like yours. I also run an RK2.

[sanababit]

bertoni, space meaning not enough water to keep ph stabilized??? and nutrients could mess with my ph too???, i read that the ph i have is not that bad but i just wanted it to stabilize a bit, question will co2 raise ph or lower it?? and calcium would lower it or raise it, currently im dosing a lot of ca to keep it at 440 ppm and stopped dosing alk because i ran out, please help me out on this, thanks

sana

[sanababit]

ebisan how is your RK2 working out for you?, have any problems????

sana

[bertoni]

Nutrients don't change the pH very much directly, but the macroalga will need them to grow. No growth means no CO2 consumed, which means the pH doesn't get changed. By space, I mean the macroalga must have room to grow.

CO2 lowers the pH, and calcium chloride supplements won't affect it.

[sanababit]

cool, i understand now, bertoni what brings your ph up then??? would kalk do it??? im just starting on this and sometimes i get mixed up , btw do you have the site or page i can take a look on more about kalk and co2 interaction on my aquarium, i will in the future install a cal reactor with co2 so i dont have to supplement it with 2 part anymore, thanks

sana

[bertoni]

I do run a kalk drip, and I have a lot of aeration in my tanks, so they seem okay. They tend to run a bit high, actually, since I like macroalgae. Sigh.