Help understand a pH increase from 7.9 to 8.6 in 6 weeks

[MikeTheNewbie]

Hello reefers and reef chemists, as the title says, I'm trying to understand the possible causes for this trend I'm seeing in my pH.
Around 6 weeks ago, my pH was swinging between 8.1 and 8.2 and now it is between 8.39 and 8.55. I recently lost 2 corals and other 2 are looking bad. I wonder if this could be one of the causes.
I hope you can help me narrow down the cause and share possible solutions. I'm considering changing from Sodium Carbonate to Sodium Bicarbonate although I'm not sure if that will help.
I have a detailed log of parameters and all the changes I do to my tank so if any other info can help, I'll be happy to elaborate.

I use 3 different methods to test for pH (Apex, Alkatroinc, Hanna) and although they don't match exactly, they all agree on the upward trend

I don't seem to have much problems with CO2 in my basement and it doesn't seem to have much relation with the pH in my case.

I have been dosing BRS Sodium Carbonate and Calcium Chloride along with Tropic Marin trace A and K since September.
Around October, I finally dialed in my Sodium Carbonate dosing to 42ml/day. This upward trend I refer to started since October.

The white and blue lines show Alkalinity which as you can see stabilized around October. I'm aiming to keep it between 8 and 8.5
The yellow bars are the amount of Sodium Carbonate dosed per day, as you can see around October I started steadily dosing 42ml/day. For the past few weeks, I've been skipping doses and manually correcting with Sodium Bicarbonate.

My parameters this week are:
Salinity: 34.8 - 35.0 ppm
Temp: 76.4 - 77.4 F
pH: 8.3 to 8.54 (Hanna says 8.6)
Alk: 8.2 to 8.3 dKH
Calcium: 450ppm
Nitrate: 15.9ppm
Phosphate: 0.07ppm
Magnesium: 1540 ppm

Tagging @Randy Holmes-Farley for help, thanks in advance!

 

[MnFish1]

Hello reefers and reef chemists, as the title says, I'm trying to understand the possible causes for this trend I'm seeing in my pH.
Around 6 weeks ago, my pH was swinging between 8.1 and 8.2 and now it is between 8.39 and 8.55. I recently lost 2 corals and other 2 are looking bad. I wonder if this could be one of the causes.
I hope you can help me narrow down the cause and share possible solutions. I'm considering changing from Sodium Carbonate to Sodium Bicarbonate although I'm not sure if that will help.
I have a detailed log of parameters and all the changes I do to my tank so if any other info can help, I'll be happy to elaborate.

I use 3 different methods to test for pH (Apex, Alkatroinc, Hanna) and although they don't match exactly, they all agree on the upward trend

I don't seem to have much problems with CO2 in my basement and it doesn't seem to have much relation with the pH in my case.

I have been dosing BRS Sodium Carbonate and Calcium Chloride along with Tropic Marin trace A and K since September.
Around October, I finally dialed in my Sodium Carbonate dosing to 42ml/day. This upward trend I refer to started since October.

The white and blue lines show Alkalinity which as you can see stabilized around October. I'm aiming to keep it between 8 and 8.5
The yellow bars are the amount of Sodium Carbonate dosed per day, as you can see around October I started steadily dosing 42ml/day. For the past few weeks, I've been skipping doses and manually correcting with Sodium Bicarbonate.

My parameters this week are:
Salinity: 34.8 - 35.0 ppm
Temp: 76.4 - 77.4 F
pH: 8.3 to 8.54 (Hanna says 8.6)
Alk: 8.2 to 8.3 dKH
Calcium: 450ppm
Nitrate: 15.9ppm
Phosphate: 0.07ppm
Magnesium: 1540 ppm

Tagging @Randy Holmes-Farley for help, thanks in advance!

Excellent data!

it is kind of difficult to really 'see' whether your CO2 is affecting your pH. To me - the trend of your CO2 is down over time, though not a lot. The problem is there is so much noise in the data its hard to see. But thats one thought.

2. The pH will vary (as you know) - with light and dark periods, When you measured the pH with the Hanna - what was the pH on the Apex - and the Alkatronic?

3. I know @arking_mark had posted a calculator that can help see if one of your measurements is 'off'.

4. I would not be focusing on pH - I would try to avoid changing dosing from bicarb to carbonate, etc. I would just dial it in - and let it be. For the most part- your pH is in a good range.

5. I assume you calibrated your meters?. Again - to my eye - I do not see the same Trend with the alkatronic as the apex (i.e. to me its not rising much - and may relate to your dosing.

Hope this helps!

 

[arking_mark]

A couple of thoughts:

• If your Alkatroinc #s are correct, you're not seeing elevated pH
• The obvious answer to rising pH is Sodium Carbonale dosing
• If you have increasing photosynthetic organisms in your tank due to additions or tank maturing, you'll have higher pH during the light period
• Hanna pH is +/- 0.2
• Apex and Alkatroinc don't publish accuracy (at least based on a quick Google search)

 

[mdb_talon]

I dont really see anything that makes me think your PH is "high". I agree the trend has been up some but not thinking it is something to be concerned about.

Based off apex and alktronic your ph is on the lower side of ideal or higher side of ideal. If you use the hanna result(i sure wouldnt) then you have a reading at the end that is approaching being too high there.

I am not a big believer that a tank under normal operating conditions(and within reasonable alk levels) is going to see PH ever really get too high without something really crazy going on.

I know you dont think co2 can be related but i still would still personally do an indoor and outdoor aeration test. Always a good baseline to see PH difference on perfectly aerated water.

 

[MikeTheNewbie]

The previous charts look jittery because its 3 months worth of data (you can only see trends that way). Here are the charts for the past 7 days showing pH and CO2 more clearly.
The light cycle definitively affects the pH. pH peaks between 4 and 6pm (Lights start ramping down at 6:00pm). I see little relation between CO2 and pH in my case. I guess those CO2 numbers are low enough to not affect the tank (big basement, few people).
I calibrated all the probes last week. Yesterday's test results are Hanna Marine pH Checker shows 8.5, the Hanna pH tester shows 8.6 (the purple dot at the top of the chart). Apex shows 8.53 (blue line) and Alkatroinc 8.09 (light blue line).
I'm going to assume my tank peaks at 8.5-8.6. Is that too bad? How would high pH affect coral? I'm trying to explain 2 recent coral deaths. Maybe I should look elsewhere?
Thanks everyone for the help!

 

[arking_mark]

Look elsewhere.

Highs of 8.6 NBS isn't an issue.

If you want to see if your meters are accurate do a cup aeration test with outdoor air. If your not reading ~8.2, then something is off.