Ph drop after replacing dry with live rock?

Variant · Jan 31, 2021

I have a 4 month system that was started with dry rock and i added a cow scrubber onto my skimmer 2 weeks ago. It bumped my ph to hover between 8.3-8.5.

Then for a variety of reasons I decided to replace all the rock with fresh live rock (aquacultured in the ocean). When I did this, I noticed my ph dropped to 8.1-8.3.

Anyone know why this would happen? I even replaced the cow scrubber media with a fresh bag and same thing. Nothing else has changed in the tank and in my home...

Rubberfrog · Jan 31, 2021

That's a lot of changes, so it's hard to differentiate causation vs correlation. I could speculate that the new live rock is encrusted with coralline algae, limiting access to the calcium carbonate within the rock. Sounds like a good theory, but is merely speculation.

Reef. · Jan 31, 2021

You ph has hardly moved, could be down to the time of day the test was taken, test error, test margin etc to put it down to a rock change for such a small change is probably over thinking this.
You ph is still at a good level.

Variant · Jan 31, 2021

Reef. said:
You ph has hardly moved, could be down to the time of day the test was taken, test error, test margin etc to put it down to a rock change for such a small change is probably over thinking this.
You ph is still at a good level.

I have a ph sensor logging data every 5 minutes. There is a trend for sure between before and after the replacement.

I am not really worried but just curious why this happened.

Reef. · Jan 31, 2021

Variant said:
I have a ph sensor logging data every 5 minutes. There is a trend for sure between before and after the replacement.

I am not really worried but just curious why this happened.

I just think it’s hard to pin it on the rock change, the change to live rock, if it was the rock will likely make up for the slight drop.p in other ways.

Could be any number of things, my money would be on a house heating change as it’s winter, windows closed etc...this is where you say you live in Florida and have ac on 365 lol

Variant · Jan 31, 2021

Reef. said:
I just think it’s hard to pin it on the rock change, the change to live rock, if it was the rock will likely make up for the slight drop.p in other ways.

Could be any number of things, my money would be on a house heating change as it’s winter, windows closed etc...this is where you say you live in Florida and have ac on 365 lol

Im in socal and leave the windows open haha. I did wonder if the bacterial diversity coming in from the live rock compared to the dry rock are more prolific and therefore consume more o2 as they propogate?

Reef. · Jan 31, 2021

Variant said:
Im in socal and leave the windows open haha. I did wonder if the bacterial diversity coming in from the live rock compared to the dry rock are more prolific and therefore consume more o2 as they propogate?

reminder to self, check avatars for clues before commenting lol

Maybe tag Randy to comment, his comments are more scientific than my bad guess work.

Variant · Jan 31, 2021

@Randy Holmes-Farley any ideas on what could be going on? Below are some more details.

When I added the co2 scrubber to the dry rock system the PH went up to a daoly swing between 8.3-8.5. In reaction to this I jad to significantly up my alkalinity doseage along with CA and MG. I use ESV dosing and no calcium reactor. I also dont run an algae reactor. Super simple with just a skimmer and some actibated carbon.

What has changed was that a couple days ago I replaced the dry rock with fresh aquacultured live rock from FL. Pretty straightforward swap. I had the live rock in a separate tank prior to this for 3 days doing 100% water changes to reduce any negative impact once i did the swap.

So now i do the swap and the next day check alkalinity and it went from my stable 7.3-7.4 to 7.8 and slowly climbing. So i reduce my dosing and check my sensor data and behold my ph had dropped to a daily swing of 8.1-8.3. I thought that maybe the co2 scrubber suddenly exhausted itself and I swapped it. After the swap no change (kind of regret swapping aince this probably meant the original co2 media was perfectly fine).

Not concerned abojt the lower ph but just curious what might be happening. I decided to swap to live rock due to dry rock troubles so I am keen on learning more.

taricha · Jan 31, 2021

Variant said:
Not concerned abojt the lower ph but just curious what might be happening. I decided to swap to live rock due to dry rock troubles so I am keen on learning more.

since we're just wildly speculating here (not enough data to do much else).
The live rock will be loaded with organisms - some of which will survive in the tank, and many others will die. This initial die-off might lower pH (decomposition etc.)

Variant · Jan 31, 2021

taricha said:
since we're just wildly speculating here (not enough data to do much else).
The live rock will be loaded with organisms - some of which will survive in the tank, and many others will die. This initial die-off might lower pH (decomposition etc.)

How does decompoaition lower ph? If you have a link to a good read on this that would be cool to read

AltitudeAquarium · Jan 31, 2021

It is my opinion that adding live rock introduced "stuff" that caused respiration and decomposition that produced organic acids in which the buffering capacity at that moment did not neutralize it simultaneously as your measurements of pH. Just a guess!

taricha · Jan 31, 2021

Variant said:
How does decompoaition lower ph? If you have a link to a good read on this that would be cool to read

When Organics are broken down by bacteria, CO2 and sometimes organic acids are produced. Both would reduce pH.
I'll poke around and see if I can find a link to some reading material.

taricha · Feb 1, 2021

Variant said:
How does decompoaition lower ph? If you have a link to a good read on this that would be cool to read

Randy's article on ammonia. See the section on ammonia produced by bacterial digestion of organics.
(CH2O)106(NH3)16(H3PO4) + 106 O2 -> 106 CO2 + 106 H2O + 3 H+ + PO4--- + 16 NH3

a bunch of CO2, and also some H+ ions are produced.

For details on the organic acids, discussion of anaerobic digestion(wiki) covers it more.
see sections on acidogenesis and acetogenesis.

certainly if dead stuff is in crevices of rock, then much of the digestion of it will be anaerobic. So both aerobic and anaerobic occur.

Randy Holmes-Farley · Feb 1, 2021

Fresh bare rock or sand also can precipitate some calcium carbonate it, which tends to lower pH for a while. I tracked that once when I added a large amount of new oolitic aragonite.

Variant · Feb 1, 2021

Thanks @taricha and @Randy Holmes-Farley ! Learn something new everyday.

If the hypothesis is that there is decomposition driving ph down, then presumeably, the ph will go back to its higher swing once the decomposition is complete? Assuming all else is constant?

taricha · Feb 1, 2021

Variant said:
then presumeably, the ph will go back to its higher swing once the decomposition is complete?

Yep. If it's die-off, then the normal pattern should return in a week or two.

EuphylliaAddict · Feb 23, 2021

Variant said:
I have a 4 month system that was started with dry rock and i added a cow scrubber onto my skimmer 2 weeks ago. It bumped my ph to hover between 8.3-8.5.

Then for a variety of reasons I decided to replace all the rock with fresh live rock (aquacultured in the ocean). When I did this, I noticed my ph dropped to 8.1-8.3.

Anyone know why this would happen? I even replaced the cow scrubber media with a fresh bag and same thing. Nothing else has changed in the tank and in my home...

Ph will drop due to the amount of bio mass the live rocks add.... Basically the bacteria is stripping the oxygen if I understand the cycle right. Good luck friend.

Variant · Feb 23, 2021

EuphylliaAddict said:
Ph will drop due to the amount of bio mass the live rocks add.... Basically the bacteria is stripping the oxygen if I understand the cycle right. Good luck friend.

Wanted to close the loop on this. The ph did climb back up to my "normal range". It took 1-2 weeks. Case Closed.