Alkalinity & ph

[brianisoutside]

How much does alkalinity effect ph?

I’ve gotten lazy in the last couple weeks and haven’t been testing much. Started to notice corals not happy. So I ran thru everything. Alkalinity fell to 6, whoops.

If I was running a PH probe would it have shown?

 

 

Sent from my iPhone using Tapatalk

[DaJMasta]

Probably not.  Alkalinity does help buffer pH up, but you have to get it pretty depleted for the pH to drop just because of that.  6 isn't a terrible range, though it's low, but the corals are probably reacting to the swing more than they are the specific number.


That said, if you supplement your alkalinity with lime water or soda ash, both of which also raise pH, maybe the lack of dosing (if that was the cause) would show up on a pH meter.

[brianisoutside]

Probably not.  Alkalinity does help buffer pH up, but you have to get it pretty depleted for the pH to drop just because of that.  6 isn't a terrible range, though it's low, but the corals are probably reacting to the swing more than they are the specific number.


That said, if you supplement your alkalinity with lime water or soda ash, both of which also raise pH, maybe the lack of dosing (if that was the cause) would show up on a pH meter.

Thanks for the help. I do dose all for reef 75 ml per day. I was noticing my montipora seemed to be growing more than normal, guess it soaked up some alkalinity. I have an acan colony melting though :/
I just added AFR over the last couple hours and got my alk up to 7


Sent from my iPhone using Tapatalk

[DaJMasta]

Is the acan somewhat new to the tank?  I had a couple of frags which looked nice for a few weeks, started to recede, and then turned around and started growing properly as they got acclimated to my system - I sort of suspect it was lighting related, but not totally sure.

Also be on the lookout for anything that may nip at them, acans seem to be pretty prime targets for nipping.

[Origami]

A pH probe taking a static (single) measurement would not give you any real hint of reduced alkalinity. However, one that plotted the alkalinity measurement over time (e.g., hour to hour, day to day, and week to week) can give you an indication that alkalinity is decreasing. Aquarium controllers like the Apex collect and display this sort of data. It's one of the ways I can tell if the CO2 in my calcium reactor cylinder has emptied. (I could look at the gauge, of course, but I can't tell you how many times it took looking at the pH curve to tell me that I needed to swap out cylinders.)

 

pH has a daily diurnal cycle that rises during the day as CO2 is consumed by photosynthesizing zooxanthallae in the coral flesh. At night, photosynthesis shuts down and the coral polyps go into respiration mode - that is, they breathe oxygen and release CO2. The increase in CO2 causes the pH in your tank to drop overnight. Thus, a plot of tank pH over time looks like a sine wave of sorts, bottoming out in the early morning before the lights come on and peaking sometime during the day when the lights are brightest (typically close to when the lights go out).

 

If alkalinity were relatively constant in your tank, this rise and fall (i.e., diurnal variation) would oscillate around a horizontal trend line. But, when alkalinity falls, the trend line of the diurnal variation is downward (toward more acid). Likewise, if alkalinity were accumulating, this trend line would be upward (toward more basic).