Magnesium and pH

[miggs76]

Question for those of you into chemistry.....I recently got a pH probe. For the first few days I saw big swings in pH (by about .25 or so throughout the day/night). I tested out my magnesium which was a little low at about 1250. I then dosed mag to get it up to about 100 to 1350 in the next few days. Now the pH is is only fluctuating by about .1 throughout the day/night. By keeping mag in check does that help keep pH stable, or is this just coincidence? PS. It is a lab grade pH probe and yes I calibrated it. Thanks in advance.

Edited April 30, 2013 by miggs76

[jamal]

adding magnesium stabilized your alkalinity which more directly affects ph. if you see swing you should check that number and see what it is. really you should always be checking it.

[miggs76]

I check alk daily.

[jamal]

what is that number. magnesium keeps cal and alk stable it is not directly responsible for ph buffering

[miggs76]

about 9dKH...calcium about 430. I dose twice a day to keep those numbers stable, and I'm installing dosers in a few days to automate it.

[jamal]

what about oxygen levels. is ur tank near windows that are leaking air.

[Origami]

100 ppm of additional magnesium at these levels will have little effect on calcium / alkalinity saturation. I'm more inclined to believe that the probe settled, there's more fresh air (or less CO2) around the tank, or something has changed with light around the tank that is affecting photosynthesis rates. What are the pH values you were getting before and after?

 

(Sent from my phone)

 

 

[miggs76]

Tank is in my basement. Near a window, but the window is never open. What do you mean by the probe "settling"? Light schedule hasn't changed.

[miggs76]

Also, not sure if it matters, but it is an open top rimless (with a screen)

[miggs76]

100 ppm of additional magnesium at these levels will have little effect on calcium / alkalinity saturation. I'm more inclined to believe that the probe settled, there's more fresh air (or less CO2) around the tank, or something has changed with light around the tank that is affecting photosynthesis rates. What are the pH values you were getting before and after?

 

(Sent from my phone)

 

Before I was topping out at about 8.10 and it would swing early in the morning to about 7.85. Now it tops out at about 8.25 and only swings to about 8.12

[Origami]

How old was the probe when you saw it swinging widely? When I say "settling" I refer to the first day or so after a new probe is entered into the water. Probes are supposed to be shipped to you wet, and their tips are often kept that way in a solution at a pH of about 4. Sometimes some of this is lost and the probe tip dries up a little. It can take a day or so for it to settle in. It's best also to go ahead and recalibrate the probe after this time for that reason.

 

If a lot of light comes from the window, it can come into play if it is a substantial source of energy for photosynthesis. I rather doubt that 's the case here.

 

Has anything else changed? Has the location of the probe changed? Have you added any electronic equipment? Did you change how the probe's wire is routed? If none of these apply, I wouldn't worry too much about it. Just recalibrate the probe and continue to observe.

[miggs76]

The probe was swinging for the first few days. It was shipped with a wet cap. Ok, I'll re-calibrate tonight. The ONLY thing I did differently was raise the magnesium.