Why is my pH chronically low, and what (if anything) should I do about it?

[eag]

My pH has been low for a very long time - hovering around 7.7. I've read that 7.8 is the lower bound of "fine" so I've been wanting to raise it for some time.

I've also had low alk for a long time... In the range of 5.7-6.5 or so. I read Randy's article on low pH which named low alk as a contributing factor. So, I tried raising alk w baking soda hoping to kill two birds with one stone. It worked well for a couple days, then all of a sudden my pH crashed again - this time really low:

I did some maintenance around the time of the big drop. Super glue, epoxy putty, some Carib sea reef rubble.

Now, my alk is corrected (8.6) but my pH is low again! I can tell that the corals really don't like the slide. At the higher pH levels, I feel like my corals were happier. Should I be trying to correct this, and if so how? What might cause something like this?

Here is an updated picture showing what my pH has looked like since that event:

 

[eag]

The spike around June 8 was a water change

 

[paul01609]

Stability is always key I wouldn’t chase numbers,could raise ph by opening a window,take a air line from your skimmer through to the outside or even a co2 scrubber

 

[eag]

Stability is always key I wouldn’t chase numbers,could raise ph by opening a window,take a air line from your skimmer through to the outside or even a co2 scrubber

Even if it is reaching 7.5 at night?

When I noticed the pH taking a dive, I opened a window next to the tank. It did help a little bit but not a ton.

I have a reefer 170. The skimmer is off and has been for some time. Maybe the exchange isn't good enough? I had low pH before I turned it off too, and it wouldn't explain the big crash

 

[eag]

It's these kinds of comments that make me worry about it being so low all the time: https://www.reef2reef.com/threads/low-ph-dissolve-corals.356097/#post-4417670

 

[kyleinpdx]

When was the last time the ph probe on your apex was calibrated? I wouldnt do a thing until I'm positive the number the apex is spitting out is legit.

 

[eag]

Ok, good point. I will try a different test. I've only had the Apex for two months and I calibrated it when I got it.

 

[DaneGer21]

Could there be air bubbles collecting around the probe?

 

[CindyKz]

If your alk is where you want it (seems to be now) I would focus on that, and not worry too much about pH.

 

[AZMSGT]

Your PH isn’t terrible and you need to remember it’s based off oxygen and CO2 as well. Is your home sealed tight and how many people and pets do you have?

How much O2 are you putting into the water? Skimmer? Surface water breaking and adding O2?

When was the last time you cleaned your PH probe? What does it read in your calibration fluid?

 

[Nilo S]

My PH increased by 0.3 after I added a DIY CO2 scrubber (small room)

 

[eag]

When was the last time the ph probe on your apex was calibrated? I wouldnt do a thing until I'm positive the number the apex is spitting out is legit.

Ok I tested with a cheap API kit and it appears that the Apex isn't far off :-/. The lighting is bad but it definitely appeared to take on a yellow tinge. Certainly the lightest color I've ever seen that test produce.

Could there be air bubbles collecting around the probe?

I gave the probe a shake for good measure, but it didn't change much. It's in my sump, there aren't many bubbles that reach the location it's placed in.

If your alk is where you want it (seems to be now) I would focus on that, and not worry too much about pH.

Everyone always says that, but what about Randy's comment that I linked to? There are plenty of places that cite pH lower than 7.8 as being potentially harmful to animals, so why don't we want to worry about it?

Your PH isn’t terrible and you need to remember it’s based off oxygen and CO2 as well. Is your home sealed tight and how many people and pets do you have?

How much O2 are you putting into the water? Skimmer? Surface water breaking and adding O2?

It's a fairly breezy apartment with only two people. There is no AC so there's plenty of air vents. I just opened the window in that room again to see how much it will move, but it didn't have too much of an effect last time I tried.

The surface ripples, but as I wondered above I suppose it could be an exchange problem.

I'm surprised to hear you think it isn't terrible - I definitely feel like 7.5 is terrible!

 

[Ernie C]

I know everyone's tank is different and you should definitely not chase numbers, particularly PH if other levels are good, but i understand and had the same issue. This is how I got my PH to stay between 8.1-8.3. I ran a airline into a good sized skimmer (reef octo) from the outside and eventually added CO2 absorbent media and I also use Kalkwasser as my top off and dose it hourly. Kalk is my main Alk and calcium source and i supplement a bit with 2 part. I used to only use the Kalk and 2 part and that had me at 7.8-8.15 The CO2 absorbent media got me to the higher range of 8.1 - 8.3

 

[Miller535]

In Randy's article, he outlines a test you can do by taking a glass of tank water and aerating it. This tells definitively tells you if you have a CO2 problem. Ph is mainly determined by CO2, O2, and alk. There's not a lot of things that affect it.

 

[eag]

In Randy's article, he outlines a test you can do by taking a glass of tank water and aerating it. This tells definitively tells you if you have a CO2 problem. Ph is mainly determined by CO2, O2, and alk. There's not a lot of things that affect it.

I will give this a shot

 

[kyleinpdx]

I will give this a shot

This is a good next step. Just in case its not handy here is the process and Randy's article.

The Aeration Test

Some of the possibilities listed above require some effort to diagnose. Problems 3 and 4 are quite common, and here is a way to distinguish them. Remove a cup of tank water and measure the pH. Then aerate it for an hour with an airstone using outside air. The pH should rise if the pH is unusually low for the measured alkalinity, as in Figure 3 (if it does not rise, most likely one of the measurements (pH or alkalinity) is in error). Then repeat the same experiment on a new cup of water using inside air. If the pH rises there too, then the aquarium pH will rise with more aeration because it is only the aquarium that contains excess carbon dioxide. If the pH does not rise inside (or rises very little), then the inside air contains excess CO2, and more aeration with that same air will not solve the low pH problem (although aeration with fresher air should).

 

[AZMSGT]

When was the last time you cleaned your PH probe? What does it read in your calibration fluid?

You never answered this question. The part that I really am interested in is what does your probe read when it's placed in the calibration fluid? So if your Cal fluid is 7 and your Probe reads 6.8 then that .2 difference brings things into perspective.

As for your readings. 7.6 - 8.4 is ideal. Your graph shows 7.55 - 7.75 which is still safe. Your API test shows 7.7ish again, still safe.

I think you need to really check the probe and make sure it's still calibrated.

 

[Randy Holmes-Farley]

You never answered this question. The part that I really am interested in is what does your probe read when it's placed in the calibration fluid? So if your Cal fluid is 7 and your Probe reads 6.8 then that .2 difference brings things into perspective.

As for your readings. 7.6 - 8.4 is ideal. Your graph shows 7.55 - 7.75 which is still safe. Your API test shows 7.7ish again, still safe.

I think you need to really check the probe and make sure it's still calibrated.

You are suggesting that pH 7.6 is "ideal"? Aragonite skeletons will slowly dissolve in a reef aquarium at that pH.

 

[AZMSGT]

You are suggesting that pH 7.6 is "ideal"? Aragonite skeletons will slowly dissolve in a reef aquarium at that pH.

How about not criticize me and help the OP? If I'm wrong.. OK, I'm wrong. But don't just come here and splatter me with a single one liner. I'm trying to help the guy. I have only the knowledge on the web to work with. You're the Chemist and Moderator.

 

[Randy Holmes-Farley]

How about not criticize me and help the OP? If I'm wrong.. OK, I'm wrong. But don't just come here and splatter me with a single one liner. I'm trying to help the guy. I have only the knowledge on the web to work with. You're the Chemist and Moderator.

I am helping the OP and everyone reading this thread by asking you to clarify what I consider to be a misleading and incorrect statement.

Before your statement, I made the decision that others had provided perfectly reasonable answers and did not think that I needed to add a comment that I agreed with them.