Acceptable Ph swing?

[Joe Batt]

We try and minimise the Ph swings with reverse cycle lighting and even feeding the skimmer with outside air etc etc.

However, what is the range of an acceptable daily Ph swing for SPS/LPS corals?

 

[Randy Holmes-Farley]

pH And The Reef Aquarium
http://www.reefedition.com/ph-and-the-reef-aquarium/

The Daily pH Swing

One of the first things that aquarists who measure pH notice is that the pH changes from day to night in coral reef aquaria. This diurnal (daily) change in pH in reef aquaria occurs because of the biological processes of photosynthesis and respiration. Photosynthesis is the process whereby organisms convert carbon dioxide and water into carbohydrate and oxygen. So there is a net consumption of carbon dioxide during the day. This causes many aquaria to become deficient in CO2 during the day, raising their pH.

Likewise, all organisms also carry out the process of respiration, which converts carbohydrates back into energy. In the net sense, it is the opposite of photosynthesis, producing carbon dioxide and reducing pH. This process is happening continuously in reef aquaria, but is most evident at night when photosynthesis is not pushing pH upward.

The net effect of these processes is that pH rises during the day and drops at night in most reef aquaria. This change varies from less than a tenth of a pH unit, to more than 0.5 pH units in typical aquaria. Complete aeration of the aquarium’s water will entirely prevent this diurnal pH swing, by driving out any excess carbon dioxide or absorbing carbon dioxide when deficient (assuming the carbon dioxide levels in the home air are steady). In practice, equilibration of carbon dioxide by aeration is difficult, and this goal is not often attained. Consequently, the pH does change between day and night.

Higher alkalinity implies more bicarbonate and carbonate in the water, and together these serve to buffer the water against pH changes (that is, they resist the change in pH as additional acids or bases are added). So the higher the alkalinity, the lower the diurnal pH swing. Also, the higher the pH, the more effective is the buffering provided by bicarbonate and carbonate in seawater (up to about pH 9), so the higher the average pH, the smaller the diurnal swing. Additional chemicals in the water also help to reduce the pH swing; borate, for example, buffers against pH changes.

With that all said, however, I do not believe that the actual change in pH each day is particularly important. I won’t go into the reasoning behind this claim here, other than stating that it is my opinion, based on my understanding of how most organisms control their internal pH, but I do not believe that diurnal pH changes that stay within the range of pH 7.8 to 8.5 are particularly stressful to most reef organisms. That is, these changes are no more stressful than being at the same pH all day. A constant pH of 7.9 may be worse for many organisms than a pH that varies from 8.0 to 8.5 each day. Of course, if the diurnal swing takes the pH outside of this range, i.e., below 7.8 or above 8.5, then certain processes take place that should be corrected, as detailed below.

 

[Joe Batt]

Thank you Randy

 

[Willie Villasana]

This makes so much more sense now. Thank you, I'm glad I came across this thread.

 

[Willie Villasana]

This makes so much more sense now. Thank you, I'm glad I came across this thread.

 

[Willie Villasana]

This makes more sense now, thank you. I'm glad I came across this old thread.

 

[ckalupa]

If you want to minimize the swing, bRS is selling their CO2 reactor chamber with hose for about $31 right now. Attach to the skimmer air inlet. Add the color changing media. When I started that I immediately saw that I never went below 8.00 anymore. That same night. And dayside I started to get near 8.3. Alk consumption went up remarkably.

 

[Randy Holmes-Farley]

If you want to minimize the swing, bRS is selling their CO2 reactor chamber with hose for about $31 right now. Attach to the skimmer air inlet. Add the color changing media. When I started that I immediately saw that I never went below 8.00 anymore. That same night. And dayside I started to get near 8.3. Alk consumption went up remarkably.

Did it really reduce the swing, or just raise the minimum and the maximum together?

 

[rob safron]

I use a CO2 reactor as well as I have a refugium running opposite lights. I give up. My day Ph is 8.3 and night 7.83 regardless.

 

[ckalupa]

@Randy Holmes-Farley it shifted the range mostly. However it did also seem to tighten it up a bit as I would previously see it range 7.78 to 8.1 area and after adding the reactor it has been running 8.01 the lowest to 8.22 as the recorded high (apex). So it is a bit tighter but not enough to write home about IMO. Just the lows dont go as far down as before

 

[Randy Holmes-Farley]

@Randy Holmes-Farley it shifted the range mostly. However it did also seem to tighten it up a bit as I would previously see it range 7.78 to 8.1 area and after adding the reactor it has been running 8.01 the lowest to 8.22 as the recorded high (apex). So it is a bit tighter but not enough to write home about IMO. Just the lows dont go as far down as before

Thanks for the update.

The reason it may have tightened is rather chem-tecky, but the pH buffering in a reef tank is highest at the high end of the pH range we encounter, and lower as the pH drops (until you get down below 7).

Buffering (from my article below):

pH 8.5 buffering = 1.2 meq/L/pH unit
pH 8.2 buffering = 0.82 meq/L/pH unit
pH 7.8 buffering = 0.42 meq/L/pH unit

Twice the buffering would mean half the pH change for the same CO2 added or removed.

I discuss that here:

https://www.advancedaquarist.com/2002/12/chemistry

 

[Gregg @ ADP]

With that all said, however, I do not believe that the actual change in pH each day is particularly important. I won’t go into the reasoning behind this claim here, other than stating that it is my opinion, based on my understanding of how most organisms control their internal pH, but I do not believe that diurnal pH changes that stay within the range of pH 7.8 to 8.5 are particularly stressful to most reef organisms. That is, these changes are no more stressful than being at the same pH all day. A constant pH of 7.9 may be worse for many organisms than a pH that varies from 8.0 to 8.5 each day. Of course, if the diurnal swing takes the pH outside of this range, i.e., below 7.8 or above 8.5, then certain processes take place that should be corrected, as detailed below.

Agreed.

Plenty of pH swings in nature, particularly in near-shore reefs. If pH moving from 8.1 to 7.8 was harmful to corals, I don’t think there would be many reefs out there.

 

[Randy Holmes-Farley]

Agreed.

Plenty of pH swings in nature, particularly in near-shore reefs. If pH moving from 8.1 to 7.8 was harmful to corals, I don’t think there would be many reefs out there.

A natural reef cannot thrive in sub-optimal conditions? Many organisms live on the environmental limit of their species, but might do better in different conditions.

 

[Gregg @ ADP]

A natural reef cannot thrive in sub-optimal conditions? Many organisms live on the environmental limit of their species, but might do better in different conditions.

Right. That’s what I was saying. I was agreeing with you.

We strive for this totally balanced, stable, unchanging system with our aquariums, when such stability doesn’t exist in nature.

 

[Randy Holmes-Farley]

Right. That’s what I was saying. I was agreeing with you.

We strive for this totally balanced, stable, unchanging system with our aquariums, when such stability doesn’t exist in nature.

I guess my point is they may do even better (grow faster, be less prone to disease, whatever) than just be OK.

 

[Gregg @ ADP]

I guess my point is they may do even better (grow faster, be less prone to disease, whatever) than just be OK.

Yessir, for sure.

We then get into the conversation of optimality vs being within upper and lower thresholds. Clearly, optimal is best. In my experience, and I think this is what you alluded to in your post I first replied to, is that ‘optimal’ might be a little more broad and flexible than we assume, and that pH movement up and down is natural and corals are well built to handle them.

 

[Jrsyhomegrown87]

I know this thread is old, but I recently discovered a nifty device sold from a guy on fishofhex. It’s a closed loop co2 scrubber, lengthens the life of co2 scrubbing material, and makes the highs higher and lessens the drop even more. Great product for sure.

 

[Randy Holmes-Farley]

I know this thread is old, but I recently discovered a nifty device sold from a guy on fishofhex. It’s a closed loop co2 scrubber, lengthens the life of co2 scrubbing material, and makes the highs higher and lessens the drop even more. Great product for sure.

I’m not a fan of closed loop scrubbers if what is meant is recycling the skimmer air because it removes a benefit from the skimmer: oxygenation at night when it tends to be lowest.

 

[SneaksMcdoogle]

Bump for those to read. This was enlightening