Why is my Ph low?

sandfan85 · Dec 21, 2020

I’m having a hard time getting my Ph above 8.0 during the day when lights are on and 7.7 at night when lights are off. I do have a algae scrubber with lights running opposite of DT lights. My skimmer air intake is run outside and runs 24/7. I know better than to chase the Ph with buffers and for now have just let it be. Should I be concerned? This is a new tank of about 4 months. Here are the specifics. Btw, I’m running an Apex and Ph probe was recalibrated about 3 months ago.

Bare bottom
New dry rock (Marco)
dkh 8.0
Phos .03
Nitrates 2-3
Cal 525
Mag 1360
Salinity 1.026
Temp 77.5 - 78.5

Montiman · Dec 21, 2020

In short you should not be concerned. Your pH depression is probably due to high CO2 even though you have the skimmer air running outside.

My pH is around 7.7 even though the home is well ventilated with an ERV. Sometimes there is just no winning. Your pH is not at dangerous levels and will not lead to coral death. You would experience better growth at 8-8.4 but do not stress about it. As a new reefer with a new tank there are better things to be concerned about.

josephxsxn · Dec 22, 2020

I agree with others with a new tank don't quite worry about it yet. As you get more photosynthetic organisms they will help consume the carbon dioxides and slowly your pH range will move up. Don't underestimate the amount of gas exchange that can truly happen, most of our skimmers are still woefully undersized for the maximum amount of gas exchange that our tanks can support.

Here's a graph I like to keep around that shows CO2 alkalinity and pH and their relation to one another. If you know your pH and your alkalinity you can discover your CO2 values. Don't worry about the colors in the chart, it's for a planted tank.

Randy Holmes-Farley · Dec 22, 2020

josephxsxn said:
I agree with others with a new tank don't quite worry about it yet. As you get more photosynthetic organisms they will help consume the carbon dioxides and slowly your pH range will move up. Don't underestimate the amount of gas exchange that can truly happen, most of our skimmers are still woefully undersized for the maximum amount of gas exchange that our tanks can support.

Here's a graph I like to keep around that shows CO2 alkalinity and pH and their relation to one another. If you know your pH and your alkalinity you can discover your CO2 values. Don't worry about the colors in the chart, it's for a planted tank.

The link won't show anything and I cannot read it well as is, but if the chart is for a planted tank, it is also for fresh water, which has a different relationship than does seawater, and is not a useful tool for a reef tank.

josephxsxn · Dec 22, 2020

Randy Holmes-Farley said:
The link won't show anything and I cannot read it well as is, but if the chart is for a planted tank, it is also for fresh water, which has a different relationship than does seawater, and is not a useful tool for a reef tank.

Thanks for the information. Personally I have found it to be pretty true comparing my own values. But considering the concern I'll make a new one using CO2SYS so that it can take into account salinity and other marine elements. :+1 This way nothing shared in the future is incorrect or misleading which I didn't intent to do.

OCADS - Program Developed for CO<sub>2</sub> System Calculations

www.ncei.noaa.gov

iamacat · Dec 22, 2020

Have you had swings in your calcium and alk? A calcium that high will cause alk to drop. Alk is an important buffer for your pH. I’m wondering if we get your alk/ca balanced if it will bump your pH up closer to where you want it.
what is your salt
What do you dose
Can you provide what your alk and ca have been over the past month?

Calcium goal should be 420-450
Alk 8.5 is a safe goal

stauzin · Dec 22, 2020

I'm assuming this is a reef tank with corals in demand of alk and cal.. you could try adding kalkwasser to your auto top off, maybe even at half saturation, this would give you a ph boost. I'm currently using brightwell's kalk+2 which also adds mag and strontium. This keeps my tank nice and stable with the added ph boost.

Randy Holmes-Farley · Dec 22, 2020

josephxsxn said:
Thanks for the information. Personally I have found it to be pretty true comparing my own values. But considering the concern I'll make a new one using CO2SYS so that it can take into account salinity and other marine elements. :+1 This way nothing shared in the future is incorrect or misleading which I didn't intent to do.

OCADS - Program Developed for CO<sub>2</sub> System Calculations

www.ncei.noaa.gov

How would you know it is correct? Do you measure CO2 somehow?

Randy Holmes-Farley · Dec 22, 2020

I show a seawater appropriate graph here:

pH and the Reef Aquarium - REEFEDITION

by Randy Holmes-Farley For many aquarists, pH is not something that they have much experience with aside from their aquarium. For many, pH is almost a black box measurement: something to be considered, but whose physical meaning makes little sense to them. This article will Read more here...

www.reefedition.com

Figure 2. The relationship between alkalinity and pH in seawater with normal carbon dioxide levels (black), excess carbon dioxide (purple) and deficient carbon dioxide (blue). The green area represents normal seawater.

josephxsxn · Dec 22, 2020

Randy Holmes-Farley said:
How would you know it is correct? Do you measure CO2 somehow?

No I have been making the assumption, or more so observed the relationship on my own tank but have not quantified the values outside of alk and PH. Your point is very valid. I don't want to hijack this person's thread with my mistake

i'll make a new post for it when I get some numbers from the CO2SYS model but I would hope one can relay on as its backed by a few papers.

Randy Holmes-Farley · Dec 22, 2020

josephxsxn said:
No I have been making the assumption, or more so observed the relationship on my own tank but have not quantified the values outside of alk and PH. Your point is very valid. I don't want to hijack this person's thread with my mistake i'll make a new post for it when I get some numbers from the CO2SYS model but I would hope one can relay on as its backed by a few papers.

Great, thanks.