Low pH despite decent indoor co2 and skimmer with outside air

[trmiv]

I’ve been trying to figure out why my pH tends to be so low. According to my Apex my pH peaks at around 7.98 and drops down as low as 7.75 at night. The probe is freshly calibrated and reads 7/10 in the calibration fluids so it’s about as accurate as I can get it.

I have a co2 meter on my Apex and my average co2 is around 650ppm but does drop as low as 400-500ppm during the day since I tend to keep the windows cracked. I run an outside airline to my skimmer, I run a reverse light cycle fuge packed with chaeto and I dose b-ionic. Also I have quite a lot of surface movement with my Mp40s. My alk is usually around 8.9-9 dkh. This is a reefer 350 that is close to 3 years old and has quite a lot of coral. It just seems with all of this I should be in a more normal range of 8-8.2 or so, yet I can’t get the tank to even peak over 8.

 

[vetteguy53081]

You can add sodium bicarbonate to sump slowly but it will drop at night. If these numbers are consistent, they’re stable and acceptable

 

[Cory]

Id try the cup test with outside air. Take some tank water and aerate it with outside air outside, then test ph.

 

[trmiv]

Id try the cup test with outside air. Take some tank water and aerate it with outside air outside, then test ph.

Yea I did that. Went from 7.96 to 8.04 after 30 minutes of aeration outside. Seems low to me.

 

[Cory]

Yea I did that. Went from 7.96 to 8.04 after 30 minutes of aeration outside. Seems low to me.

30 mins? Not sure if thats enough time. Id try for 2 hours to be sure. If fully equilibriated with outside air ph should have been more than 8.2 at that dkh. If its not, it could be either a faulty ph probe, bad calibration solution or procedure, or zero boron in the water (highly unlikely)

 

[trmiv]

So after an hour outside it went from 7.79 to 8.07. I guess despite my relatively low indoor co2 and pumping outside air into my skimmer I must have poor aeration. I wonder if the small reaction chamber of my Tunze 9410 DC is part of the issue. The skimmer is so short.

 

[Cory]

So after an hour outside it went from 7.79 to 8.07. I guess despite my relatively low indoor co2 and pumping outside air into my skimmer I must have poor aeration. I wonder if the small reaction chamber of my Tunze 9410 DC is part of the issue. The skimmer is so short.

It might be too little air draw to make any difference. I use a beckett drive skimmer which helps. I also had to pump fresh air into my overlfow box, and glass lid which gave me a low of 8.1 and high of 8.3 daily. Everything is sucking from the outside 2" abs pipe i made so it doesnt reduce airflow. What sort of air draw does the skimmer have?

 

[Cory]

How are you measuring co2 from the apex?

 

[trmiv]

It might be too little air draw to make any difference. I use a beckett drive skimmer which helps. I also had to pump fresh air into my overlfow box, and glass lid which gave me a low of 8.1 and high of 8.3 daily. Everything is sucking from the outside 2" abs pipe i made so it doesnt reduce airflow. What sort of air draw does the skimmer have?

750 lph max but I only run the skimmer at around 40%.

How are you measuring co2 from the apex?

I use a Tellaire Ventostat T8100D CO2 controller hooked to the ASM module.

 

[arking_mark]

A couple of thoughts...

So assuming your Alk and CO2 measurement are correct, your expected pH should be 8.13 NBS.

Looking at your cup aeration test with outdoor air and getting 8.07pH would indicate your meter is still inaccurate. Outdoor aeration with 8.9dKH water should be between 8.25 and 8.3 depending on your air quality.

Now with regard to your skimmer. You really need to oversized skimmer to outcompete your powerheads and return flow to see appreciable pH impact.

That brings us to your tank aeration. I would recommend doing a proper cup aeration test. Test your cup with an airstone next to your tank. If your cup next to your tank is higher in pH, you need more tank aeration. The outdoor test lets you know if you have elevated CO2 in your home (most do).

Let us know what you find...

 

[trmiv]

So i calibrated another ph monitor I have (pinpoint) and it’s reading about .12 higher than the Apex. Today with the windows open the Apex peaked at 8.08 and the pinpoint peaked at 8.2. The pinpoint seems closer to reality to me given my indoor co2

 

[arking_mark]

So i calibrated another ph monitor I have (pinpoint) and it’s reading about .12 higher than the Apex. Today with the windows open the Apex peaked at 8.08 and the pinpoint peaked at 8.2. The pinpoint seems closer to reality to me given my indoor co2

Sounds about right. Unfortunately, our hobby grade meters aren't great.

Post in thread 'Aquarium pH Distilled' https://www.reef2reef.com/threads/aquarium-ph-distilled.853474/post-9330359