pH swings and water volume

[reefkeeper2]

Like most people my tank has a daily pH swing. I have done a lot to minimize it like plenty of aeration with fresh air, kalk additions and a ATS on an opposite light cycle. Lately even all this doesn't seem to be enough. I think there is just so much living stuff in the display that when lights go out there is not much I can do to keep the pH from dropping like a rock. My next plan is to increase the water volume down in the sump by 200 gal or so. ( the display is 427gal) . I'm not certain this will help however. My thinking is that with a larger volume of water, when the lights go out it will take more time for the pH to fall. More volume = more stability. Am I right?

[HighlandReefer]

There are Reef Tanks of the Month with some very nice coral, well above average, who have pH swings dropping down to 7.8 and show no adverse effects to their occupants. ;)

"Dec 08 TOTM", Sounds like yours may very well be one of these tanks as well. :)

The Nutrient Dynamics of Coral Reefs (by Chris Jury):
Part IV, The Sky Above
http://reefkeeping.com/issues/2006-12/cj/index.php

From this article:

"Also, the pH on most coral reefs (especially in shallow areas such as reef flats) is usually not constant over a 24-hour period. In fact, the pH on a reef flat may vary from less than 8.0 to more than 8.6 within 24 hours with no significant deleterious effects on the animals. Sometimes it is stressed that all water parameters in a reef aquarium must be kept very stable to have success. If this were true about pH (and many other parameters), then nature would be failing miserably at growing reef organisms. Reef animals can easily tolerate a daily pH fluctuation. The reason for the fluctuation in pH on reefs, just as in reef aquariums, is that during the day the rapid consumption of CO2 by photosynthesis reduces its concentration faster than it can diffuse into the water from the atmosphere, while at night community respiration with no consumption due to photosynthesis raises the amount of CO2 in the water faster than it can diffuse out to the atmosphere. Calcification also continues at night in corals, though at about one-half to one-third its daytime rate. This is significant because calcification produces about 0.8 mol CO2 for every mol CaCO3 deposited."

[reefkeeper2]

I know that most think I shouldn't worry about a pH that dips to 7.8. However, when the pH of my tank goes that low at night I have outbreaks of STN . In my tank the two always coincide. Some of the LFS owners in my area have noticed the same phenomenon. After they takes steps to correct the low nightime pH, the problem dissapears.
I think it is a combination of factors that have to occur with the lower pH that is most likely the cause. I wish I could figure out exactly what occurs and why. At any rate, if I keep the ph above 7.9, it doesn't happen.

[HighlandReefer]

It is thought that higher alk levels may help offset low pH effects within coral (chemical reactions within coral). Chris Jury & Randy have discussed this possibility in the past.

Do you keep your alk at 7 dKH?

Keep in mind some alk kits used for freshwater and seawater may be freshwater kits which will give results about 10% lower than actual. So at dKH 7, the alk level would be actually around 6.3 dKH when using one of these alk kits. I thought I would at least mention this. Then there may be some test kit error which is likely with hobby grade kits. Also, there will be greater pH swings at lower alk levels. ;)

[reefkeeper2]

No, 7 is a little low, especially if you want to keep the pH up. This morning it was at 8.5 which is where I like to keep it. I could bring it a little higher and that would help. I don't like to stray too far from NSW levels if I can help it.
I'm using the Hanna Alk Checker. I like the reproducability of the results I get over the other kits I have tried.

[HighlandReefer]

There have been hobbyists who have reported your findings, especially with very low nutrient content in the water, including low phosphate, low nitrate and low dissolved organic carbon levels. You can't measure the DOC with any hobby grade tests. If your DOC is low, than you will get the same results as you are seeing with your coral per research I have read. It's hard to figure out what causes this problem with all the unknowns. Certainly pH could be a possiblity as well, especially since you are seeing results only when your pH drops. I'm just throwing things out here that may play into the equation. Perhaps low DOC and low pH can have adverse effects when combined as well. Certainly not all hobbyists with low pH problems show these effects, just some of them.

[reefkeeper2]

Cliff, what do you think about my original question? Do you think an increase in water volume would moderate the pH swing at all?

[HighlandReefer]

I have low pH problems due to excess CO2 levels in the house like many. I have increased my tank volume and it did not help with the pH low. You have more water, but you also have more CO2 that will dissolve in the water. IMHO, the CO2 level in the house, is more of the problem then the CO2 produced at night from organisms in your tank.

An algae scrubber seems promising to me from what I have read, but I have not worried about this since I don't see any negative effects myself. I don't have as many sps as many do though. ;)

[reefkeeper2]

I have an algae scrubber and the pH is a bit higher in the water below it. It is not enough of a boost however. When the lights go out the pH falls from 8.3 to 8.0 in about 2 hours. It takes the rest of the night to reach 7.8. The tank is in a sunroom, open top with all the windows open at night so I don't see how high CO2 in the room could be possible.
Here is a link to my most recent vid of my tank.
http://http://www.youtube.com/watch?v=Pfr4jAxrzgE&feature=plcp (http://www.youtube.com/watch?v=Pfr4jAxrzgE&feature=plcp)
You can get an idea of the setup and bioload.

[HighlandReefer]

Gorgeous tank. ;)

Try the test Randy Recommends in this article to distinguish the particular problem you have:


Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm

From it:

"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)."

[reefkeeper2]

OK, so this morning I took some tank water, placed it in a container with an air stone and let it bubble away for two hours. It was with inside air next to the sump in the basement. I didn't do the test next to the display upstairs because the windows in there were open all night. The starting pH was 8.0 and the finish pH was 8.01. I was very surprised. I have an exhaust fan that runs constantly in there.
Next I connected the air pump to the outside line that provides fresh air to the skimmer and all my other air pumps. In 15 minutes the pH rose to 8.09.
So it seems that even with an exhaust fan running 24/7, there is excess CO2 in the basement. I can safely assume that the same problem exists upstairs when the windows are closed.
I need to pump in more fresh air. Easier said than done.