Why is my Alk dropping but not my Ph?

[Broutilde]

Hello,
I read a lot about the relationship between Ph and Alk, and I thought I figured it out. But apparently not.
I have a AIO 25 gallons that I dose manually everyday (for now).
I keep my Alk at 8.2, which usually keeps my Ph at 8.13. It's been stable for the past 4 months (tank is 6 months old), I have a Ph monitor that I look at everyday: Ph is at 7.8 at night, and rises to 8.13 during the day.
Today I decided to measure my Alk with my Hanna checker, and discovered that it's sitting at 6.3, which is very different than the 8.2 I'm used to. Now I'm sure that it didn't happen overnight and my corals are not in distress, however I wonder how it's possible. Last time I checked my Alk was more than a week ago and it was like usual.
First I thought about the Ph probe, which I recalibrated 1 month ago. So I recalibrated it again, but that wasn't the problem.
A friend suggested precipitation but I see no trace of it on my return pumps or anything. Also my calcium is at 430 and Magnesium 1320.
He also suggested that my corals would have used the Alk which I'm ok with, but until now I thought by doing that, it would lower Ph at the same time? That's also how I was checking my levels everyday, by looking at the Ph on the monitor.
I also open my windows a lot for aeration every day. I have a skimmer but intake line is not outside and can't be.
What could cause this?
I would like to raise my Alk a bit, at least to 8 to be like before, but it's also gonna raise the Ph (which is still sitting at 8.13).
Can anyone help?
Thank you

 

[HuduVudu]

I also open my windows a lot for aeration every day.

How long have you been doing this?

I would like to raise my Alk a bit, at least to 8 to be like before, but it's also gonna raise the Ph

PH isn't static through out the day, what is your swing, or if it is easier post your probe graph.

Curious to see.

 

[Broutilde]

How long have you been doing this?


PH isn't static through out the day, what is your swing, or if it is easier post your probe graph.

Curious to see.

I've been opening my windows everyday even before acquiring a tank!

I don't have a prob graph as it's just a Ph monitor. I don't mind my Ph swing, it's been swinging from 7.8 to 8.13 everyday for 4 months now. What I don't understand is why my Alk dropped dramatically without any incidence on the Ph. Also now that my Alk is at 6.3 instead of 8 for the same Ph value (8.13), I'm afraid that raising the Alk is gonna skyrocket the Ph.

 

[HuduVudu]

I'm afraid that raising the Alk is gonna skyrocket the Ph.

This is very unlikely, and honestly your PH swings are a bit low. I would look for 8.0 to 8.3 swing.

Another question exactly what is your dosing regimin?

 

[Broutilde]

This is very unlikely, and honestly your PH swings are a bit low. I would look for 8.0 to 8.3 swing.

Another question exactly what is your dosing regimin?

I dose three majors elements separately, and replenish traces when doing a water change every two weeks. I'm about to switch to All for Reef.

 

[HuduVudu]

I dose three majors elements separately

Ca, CO3, Mg? Are they designed to work together?

What percentage of water change do you do?

 

[Broutilde]

Ca, CO3, Mg? Are they designed to work together?

What percentage of water change do you do?

20% water change.
As for the dosing, I dose bulk powders: soda ash; calcium chloride; liquid magnesium mix.

 

[HuduVudu]

I dose bulk powders: soda ash; calcium chloride; liquid magnesium mix.

What is the formulas are you using to set up your dosing regimin?

How often do you do your water changes?

 

[Broutilde]

I'm thinking...I'll double check Alk level with a different test kit, just to be sure.

 

[Broutilde]

What is the formulas are you using to set up your dosing regimin?

How often do you do your water changes?

I based my calculation on 5 days of testing, and use BRS calculator.
Like previously said, water change every two weeks.

 

[HuduVudu]

20% water change.
As for the dosing, I dose bulk powders: soda ash; calcium chloride; liquid magnesium mix.

How do you dose your magnesium?

 

[Broutilde]

How do you dose your magnesium?

Well...Manually? It doesn't really decrease (from 1350 to 1320 in one week), so I usually dose every week.

 

[CircleCityBill]

While a complex mixture of ions, the pH of the water is affected in large by the ratio of carbonate ion to bicarbonate ion. Note that it is the ratio (not the absolute quantities of the ions) that determines the pH. Alkalinity is a measure of the total concentration of alkaline ions in the solution (carbonate ion, bicarbonate ion, and others). In principle, you can lower the total absolute concentration of the alkaline ions (alkalinity) without shifting the ratio. Dissolved carbon dioxide in the water shifts the ratio towards bicarbonate ion and lowers the pH.

 

[HuduVudu]

@Broutilde Have you opened your windows lately or you or your family been absent for significant periods of time? Is the top of your tank covered, or have a hood. Have you changed any of those things recently?

 

[Broutilde]

While a complex mixture of ions, the pH of the water is affected in large by the ratio of carbonate ion to bicarbonate ion. Note that it is the ratio (not the absolute quantities of the ions) that determines the pH. Alkalinity is a measure of the total concentration of alkaline ions in the solution (carbonate ion, bicarbonate ion, and others). In principle, you can lower the total absolute concentration of the alkaline ions (alkalinity) without shifting the ratio. Dissolved carbon dioxide in the water shifts the ratio towards bicarbonate ion and lowers the pH.

What would you advise in my case to re-establish that ratio? Do you have any idea of what could have happened, as you specified that lowering alkalinity without touching the Ph is possible "in principle"?
Soda ash (which I already dose) raises the Ph quite a lot.

 

[Broutilde]

@Broutilde Have you opened your windows lately or you or your family been absent for significant periods of time? Is the top of your tank covered, or have a hood. Have you changed any of those things recently?

I really haven't changed anything honestly. I have a mesh lid on my tank. Windows are opened every day from 4pm to 8/9pm (and I'm pretty anal about my air quality, so it's EVERY DAY haha), and there's always someone at home.

 

[HuduVudu]

What would you advise in my case to re-establish that ratio? Do you have any idea of what could have happened, as you specified that lowering alkalinity without touching the Ph is possible "in principle"?
Soda ash (which I already dose) raises the Ph quite a lot.

CO2 plays a big role here. CO2 <-> Cabonic Acid (H2CO3) <-> BiCarbonate(HCO3) <-> Carbonate (CO3)

If you haven't had something die in your tank (aerobic breakdown creates Acid (H+)). Then I am going to go with coral growth. Which is good

 

[RobB'z Reef]

Following.. . This is good learning stuff

 

[Broutilde]

CO2 plays a big role here. CO2 <-> Cabonic Acid (H2CO3) <-> BiCarbonate(HCO3) <-> Carbonate (CO3)

If you haven't had something die in your tank (aerobic breakdown creates Acid (H+)). Then I am going to go with coral growth. Which is good

As I'm usually dosing soda ash to replenish Alk, and soda ash tends to increase Ph, what would you do to raise Alk without raising Ph?
Or anything else to do to re-establish this balance that I had until now?
I'm glad my corals are growing, but I'm worried that it could go on like this? What if my Alk reach 4 dkh while Ph still at 8.13?

 

[Randy Holmes-Farley]

As I'm usually dosing soda ash to replenish Alk, and soda ash tends to increase Ph, what would you do to raise Alk without raising Ph?
Or anything else to do to re-establish this balance that I had until now?
I'm glad my corals are growing, but I'm worried that it could go on like this? What if my Alk reach 4 dkh while Ph still at 8.13?

Is your pH too high? If not, I'd stick to the carbonate. Switching to baking soda (sodium bicarbonate) if you do not want any pH rise is a fine plan.

pH is determined by the carbonate alkalinity and the CO2 level in your tank, which is partly driven by CO2 in your home air. Folks can see a pH drop just from having a large party in their home, driving up CO2 levels.