pH and CO2 question

[hart24601]

I have read Randy's pH articles and have a couple of questions. I know that it is not advised to "chase" pH and a pH of 7.8 is generally considered quite acceptable and no reason to mess with it. Correct me if I am wrong, but global ocean acidification and reduced pH in our homes are caused from the same thing, CO2 levels (more or less if alk is in the NSW range). Now if we are worrying about global impact of CO2 why shouldn't this be of concern to tanks in our homes that if sealed up, have elevated levels of CO2? I am asking this because there have been, and probably will be more, studies of coral growth under higher CO2 concentrations which translate to low pH. Doing a quick search of studies it appears that low pH in the 7.8 and 7.9 region does impede coral growth. While the coral might still live, it appears to me that lower pH that has been recommended as acceptable does slow growth. Considering all the arguments we have over what goes coral faster with lights, calcium and alk levels, amino acids and such it would seem that having published results that show reduced growth should be more of an issue possibly revising the range of pH we consider acceptable for coral in our home aquaria if we want growth and color (or lack of bleaching). Here are just two studies I found:


Bleaching was increased and calcification decreased at 7.85-7.95 at temps we use in the hobby:
Ocean acidification causes bleaching and productivity loss in coral reef builders

Not as good for our purpose since the low pH was lower than what we call acceptable but still interesting as the results look pretty linear and one could use that for pH of 7.8 and show lower growth (not the best science I know):
http://sigarra.up.pt/icbas/pt/publs_pesquisa.show_publ_file?pct_gdoc_id=11431


I am wondering if it's time to revise reef pH recommendations or at least clarify a pH of 7.8 is acceptable but most likely results is slower coral growth with possibly greater bleaching.

 

[UK_Pete]

Thats exactly what I think and went through a few questions with Randy recently where he confirmed that essentially as you say tank pH is a measure of CO2 levels, with a few caveats (as you say depending on alk). I must have quite high levels of CO2 in my tank room judging by my old pH.

Maybe thats because its winter, windows and doors tight shut, with draught excluders and uPVC windows with rubber seals etc. Add the fact that we have the tank room full of several toddlers all day running around like maniacs, frequently several mums drinking tea etc, and I guess you have a high CO2 room.

I ran the skimmer intake outside and turned the air up to full (had to raise the cup) and my pH went from about 7.9 to about 8.3, sometimes even 8.4. But I must have a low metabolism tank for results like that (ie little CO2 generation in the tank, meaning probably because I dont feed much). So most of the CO2 was probably coming from the room and from the graphs I was able to find online (search my posts to find a link), I worked out IIRC I had about 1000 ppm in the room. Now tank CO2 must be only slightly greater than outside ambient (IE partial pressure of CO2 not much above 400 ppm).

 

[hart24601]

That is really interesting that running the air from outside raised the pH that much, wow, what a huge change! I recently did the same (the build link in my signature) and it definitely raised it, not that much though! Perhaps due to my amount of surface agitation from the gyre.

The issue I want to get at is that most sources of information and people on the forums say that a tank that ranges from 7.8-8 is just as healthy and grows just as fast as one that is say 8.0-8.2, but it looks like the research suggests that is not the case at all.

 

[beaslbob]

Tay I handle low ph is to balance out the tank with macro algaes so the tank becomes a net consumer of co2 and producer of oxygen each 24 hour period.
Regardless of why or how the ph was low to begin with.
I then get alk up which limits the lights out pH drop and always measure pH and alk just before light out.
For example, when I first added macro algaes to my old 55g pH went from 7.7 or lower to above 8 in a day. A week later it was up to 8.4 or higher and stayed there for years. Sickly fish in the tank recovered and thrived for years as well.
my .02

 

[UK_Pete]

Yea I was flabbergasted at the increase! Never thought such a simple mod would make such a dramatic difference, I went through several methods with long suffering Randy like scrubbers etc before trying the intake mod, a half hour job, and certainly for now its sorted. My tank is only a 55 gallon with 500 litres per hour air going in the skimmer so its probably quite heavily aerated now, which might have helped the magnitude of difference in pH, plus low food consumption means low CO2 production as I said. If I had lots of fish, or lots of nutrients and carbon input (driving lots of bacterial growth hence generating lots of CO2) it might be different. I also put a lid on the tank for the new pH tests so no air from the room could dump CO2 into the water via the water surface. The lids off now but I intend to make a permanent one for evaporation reasons, good to know the pH will stay happy.

I agree, without any qualification apart from the reports that CO2 is harming reefs, that if corals in natural reefs are affected by slight CO2 increases, then dramatic CO2 increases in reef tanks must be worse. But on the other hand people seem to be able to keep corals at what seems to me far too low a pH. Maybe other factors are contributing, maybe they are all using limewater / sodium carbonate sufficient to soak up the CO2, macro algae as Bob said, I dont know. But it can't hurt to have a more natural pH IMO so I am sticking with the outside air intake! Randy seems to say though that he feels a pH of down to about 7.9 minimum is OK IIRC, but maybe thats a real bottom figure, far from optimum but workable. Natural seems likely to be optimal though, and that means water well equilibrated with air, and in addition you have the benefit of plenty of oxygen for times when something dies and your tank oxygen demand shoots up.

Bob, interesting you said fish were helped by the increased pH too.

 

[Randy Holmes-Farley Verified Community Expert]

I think that since many reefers have fine tanks with a low pH of 7.8, they conclude that it is OK.

But that doesn't really address the fact that corals may thrive more effectively at pH 8.0 or 8.2.

I personally would try to keep the pH higher than the 7's, but I'm apparently in a minority on that.

 

[hart24601]

I think that since many reefers have fine tanks with a low pH of 7.8, they conclude that it is OK.

But that doesn't really address the fact that corals may thrive more effectively at pH 8.0 or 8.2.

I personally would try to keep the pH higher than the 7's, but I'm apparently in a minority on that.

Thanks for your viewpoint Randy! I thought you supported that there was no reason for pH to be higher than upper 7s, don't know why I thought that, perhaps because so many others say it and you are influential with reef chemistry I just assumed it came from you.

Looking at the research it appears that there is good evidence if your pH is under 8 you might want to consider using external air, scrub co2 or run a larger fuge. I was surprised with the bleaching results in the study - I wonder how many people have bleached their corals and pH was a factor.

 

[Randy Holmes-Farley Verified Community Expert]

I have told people to not overly worry about pH of 7.8, but that is different than saying it is just as good as a higher pH.

 

[that Reef Guy]

I have told people to not overly worry about pH of 7.8, but that is different than saying it is just as good as a higher pH.

So do you consider anything under 7.8 a problem?

 

[Randy Holmes-Farley Verified Community Expert]

Yes, I'd try to raise pH values that went below about pH 7.8.

 

[hart24601]

Yes, I'd try to raise pH values that went below about pH 7.8.

If the pH is below 8, is there any value in keeping alk above NSW values to try and prevent some of the effects in the papers to try and mitigate some of those issues since they found even the 7.8-8.0 range to have potential problems?

FWIW after looking at all the information I could find on this I decided it was worthwhile to keep my pH above 8. All I had to do was supplement my 2 part dosing with kalk. Easy fix for me. I just hadn't considered it before - but I really think I noticed the tank overall doing better. Coco worms started adding new material and the overall tank health seemed to increase, but there is no way I can prove the pH raise was the ticket.

 

[glb]

I have told people to not overly worry about pH of 7.8, but that is different than saying it is just as good as a higher pH.

So is it better to raise ph even if it means higher Alk numbers? An outside line isn't an option for me. I have a skimmer now, which has helped, and I dose with kalk, which helps. But I still run 7.8-8.1. I could raise it with more kalk but would that really improve the growth rate of my corals?

 

[Randy Holmes-Farley Verified Community Expert]

If you have a ULNS SPS system, you apparently need to be very careful with alkalinity,a nd I wouldn't boost it above normal levels without due care.


If you do not have such a system, then higher alk can perhaps help to both offset the effects of reduced calcification due to the low pH, and can also help to actually boost the pH.

 

[that Reef Guy]

Yes, I'd try to raise pH values that went below about pH 7.8.

Is 7.8 for the Low Part of the Day when you turn the Lights on or for the High Part when you turn the Lights off?

 

[that Reef Guy]

Yes, I'd try to raise pH values that went below about pH 7.8.

What happens if your PH goes below 7.8?

 

[Randy Holmes-Farley Verified Community Expert]

At some pH not far below pH 7.8, aragonite (e.g., coral skeletons) will begin to slowly dissolve. Also, as the pH drops, calcification becomes harder and harder for corals and other creatures.

This is why so many oceanographers are concerned about the impact on coral reefs due to the pH drop in the oceans from released carbon dioxide in the air.

 

[that Reef Guy]

At some pH not far below pH 7.8, aragonite (e.g., coral skeletons) will begin to slowly dissolve. Also, as the pH drops, calcification becomes harder and harder for corals and other creatures.

This is why so many oceanographers are concerned about the impact on coral reefs due to the pH drop in the oceans from released carbon dioxide in the air.

So the Lowest PH should ever get is 7.8 - good to know.

Now you said that Coral Skeletons will Dissolve with Low PH.

Does that mean that Zoanthids are NOT affected by PH whatsoever since they have no Skeleton? or will PH harm them as well?

Speaking of PH Drop in the Oceans I just saw this Documentary and thought it was great.

I Highly Recommend watching it.

https://www.reef2reef.com/forums/re...as-corals-suffering-low-ph-did-you-watch.html

 

[Randy Holmes-Farley Verified Community Expert]

I do not actually know what pH range most soft corals thrive in vs where they begin to suffer from being outside their norm.