New lights and ph Fluctuation

[murphy]

I just added a new lighting system to my 50 gallon about 2 weeks ago replacing my fluorescents. Dual Metal Halides 175W 10k and 2 URI 95W VHO super actinic lights. I also removed the glass top for better lighting and circulation. However, since adding the lights my ph has gone a bit wild. It has climbed to about 8.55 just before lights out and declines to 8.15 before lights on. Big range. Also I noticed my LSB is producing a lot of bubbles. The temp has increased slightly to 80 with the new lights, working on some additional fans. Otherwise other parameters are good kh 9.8, calcium 420, Mg 1380, sg 1.024. I only add B-ionic for Calcium.

One thing I am going to change is the refugium lighting cycle. I will try a reverse photoperiod, hopefully that will reduce the swing.

Just wondering if anyone has experienced this when adding new lights and whether it is just a temporary cycle that I am going through? If not, any suggestions?

[aliendomain]

reversing the photoperiod on the refugium will help. The increase in pH is due to the increase in o2 in the water from photosynthesis. Do you have allot of macro in the tank? I couldn't tell you what could be creating o2 in the sand bed but that's what I'm guessing the bubbles are. Give us an update after you have changed the timing on your refugium I know I'm curious.
Good luck!

[mapster]

aliendomain hit the nail on the head. Reversing you're photo period should help, depending on the size/stock of you fuge. If not, you could try dripping kalk after the lights go out in the display tank. With the right drip rate this should also reduce the Ph fluctuation.

[aliendomain]

Good call on the night time drip, but could that not also increase the daytime ph?

[murphy]

That is actually my worry. I do not drip anything now, but if I did, I am afraid that my ph will rise above 8.5, which is not what I want to do.

I guess my goal is to reduce the range of the fluctuation. Maybe I should try the ESV Buffer Bicarbonate.

[Jimbo]

The organics nutrients in your sand bed are being processed, once the top layer bubbles out the nutrients this should decrease. This will also decrease the o2 level in the tank. Mine still bubbles and has always done so, but at a lesser degree.

More vigorous surface agitation can help maintain the co2/o2 balance along with a good protien skimmer.

Like others have said a opposite cycle for your refugium from you MH's will help. I run my refugium opposite my MH' bulbs only. The refugium light stays on when the actinics are on. I don't believe the actinics are powerful enough to componsate alone, or even come near the photosynthetic activity that the MH produces.

You might want to try some buffer, but not too much and watch your alkalinity.

[Geoff]

i have been playing around with my light cycles on my refugium while my tank has been cycling. i have found that it is a moving target until the refugium is well stocked. my refugium is growing rapidly but not as fast as the display. if i put the refugium on reverse cycle the display starts growing algae quickly without any competition from the refugium. if i leave the refugium on constantly it seems to keep the PH the most stable, but i have seen the macro in the refugium seems to grow slower. when i put the refugium on the same cycle as the tank, the algae in the display slows down, but i get a .2 PH swing during the day. i have been noticing that as the refugium grows when it is on a reverse cycle the display algae is a little slower in growth than before. right now i have it on constantly for the weekdays and on the same cycle on the weekends. this seems to work for now.

G~

[tdwyatt]

Originally posted by aliendomain
...The increase in pH is due to the increase in o2 in the water from photosynthesis. Do you have allot of macro in the tank?

Well, Actually...

AD, the concept was in the right direction, the higher intensity of lighting does stimulate a greater rate of photosynthesis, both in macroalgae, corallines, and microalgae, and this is what is driving the change in pH, but NOT because it is increasing the oxygen level in the tank.

Photosynthesis consumes the primary agent of pH change in seawater when photosynthesis occurs. It is this removal of CARBON DIOXIDE from the water column by the photosynthetic process in plants and organisms that contain plant symbionts (like autotrophic corals) that causes the rise in pH in the water column. In the same manner, when the lights go out, photosynthetic organisms stop consuming CO2, and become net producers of CO2 along with animal respirations. This accounts for the drop in nightly pH as CO2 levels increase. Buffering by the carbonate/bicarbonate buffer system slows these swings to some extent, but is stoichemically unable to keep up with the amount of change in CO2 in a closed system the sizes of most of our aquaria and their corresponding population and plant densities. In shallow bays with poor circulation and heavy macroalgal populations, this same phenomenon occurs, but for the most part, the swings are not as pronounced in the open ocean as they are in our tanks. It is all driven by carbon dioxide and its relative presence or absence in both the water column and the atmosphere directly in contact with that body of water. Oxygen in and of itself has little if any direct effect on the pH of seawater or its carbonate/bicarbonate chemistry. In addition to the CO2 concentration, pressure, temperature, and salinity (and indirectly Ca and Phosphate) have major roles in the daily swing in pH levels. About the only effect that Oxygen has on the pH of ocean water has to do with the partial pressure that it exerts as a dissolved gas. It's presence in the water column may affect to some small extent dissolved CO2 by competing for space within the water column, but this is truly insignificant and will not play a role in living ecosystems that we keep.

The idea about photosynthesis affecting the pH is correct, but only because it removes CO2 from the water column, not because the O2 tension is increased.

My $0.02 worth (US)...

[mapster]

Thanks for the clarification TD!

Question: for reasons stated above ph drops in our tanks after the light go out. If we combat that drop by a reverse light cycle or by means of an additive, when the lights come back on, whats to stop the ph from gradualy rising day by day? Would it be better to leave it as is?

I hope that makes sense, because i have feeling what im about to type will not make any...

lets say...

ph at lights out is 8.4, this slowly drops to 7.9 over the course of the evening. Lights come back on at 7.9 and slowly raise back to 8.4 and so on and so forth. If we takes steps to reduce the fluctuation and the ph only drops to 8.2, would the ph slowly rise above 8.4 by next lights out? If thats the case it would seem easier (on the corals and on us) to do nothing rather than have to constanly battle to maintain a level ph. In a highly controlled enviorment with ph controlers, calcium reactors, kalk top-offs and such it would be as big a problem, but in a "low tech" system it may be hard to control without constant monitering.

I guess I dont understand it too well, please help.

MAP

[tdwyatt]

Originally posted by mapster
Question: for reasons stated above ph drops in our tanks after the light go out. If we combat that drop by a reverse light cycle or by means of an additive, when the lights come back on, whats to stop the ph from gradualy rising day by day? Would it be better to leave it as is? lets say...

ph at lights out is 8.4, this slowly drops to 7.9 over the course of the evening. Lights come back on at 7.9 and slowly raise back to 8.4 and so on and so forth. If we takes steps to reduce the fluctuation and the ph only drops to 8.2, would the ph slowly rise above 8.4 by next lights out?

This might be true if there were not for:

• the constant replacement of CO2 from the atmosphere
• the constant consumption of alkalinity and calcium from the water column by calcium precipitating organisms.
• the constant production in living systems of organic acids and CO2 from the metabolism of carbohydrates by living organisms
• Le Chatelier's principle (my personal fave)
• the low solubility of Calcium carbonate in seawater.

All these things control the pH of seawater, and the presence of living (hermatypic) organisms make those substances growth limiting factors due to their consumption in the process of building stony skeletons. Were it not so late here, and I didn't have to work (yet again...) tomorrow, I would explain this in depth tonight. There are many threads that explain the role of the carbonate/bicarbonate buffer system on this BBS, but here is a link to the chemistry and here is a related thread and a more involved and detailed debate on CO2 and buffer roles

For the most part, the gist of the above is that when the pH gets too high, there are reactions that occur from the buffer system that donate protons, starting from the drive of Carbonate back to bicarbonate (and in the process liberating a proton) which drive pH down. This is the role of the buffer system, it releases protons when pH gets too high, and absorbs protons when the pH gets too low. In addition, as CO2 is removed from the equilibrium, it is gradually replaced by atmospheric CO2, driving the pH back to a (saltwater normal) pH of 8.2 via its formation of bicarbonate ions. Should the alkalinity become too concentrated (yes, this can occur at depth in the ocean), then actual calcium carbonate can precipitate out of solution and remove a portion of the alkalinity due to its low solubility (which would occur if there were some extreme source of alkalinity that continued to drive pH up in seawater, we see this when we add concentrated alkalinity solutions to seawater, like part A of B-ionic)

Many mechanisms to prevent this, just too late for me to discuss them tonight.

Man, I hope that new coffee pot works tomorrow morning...

heh!!! New technology toy, it grinds it's own beans just before it brews them!

[mapster]

Ah yes, Le Chatelier's principle. How could I forget?

TD thanks for all the info, HUGE help as always!

You rock!!!

heh!!! New technology toy, it grinds it's own beans just before it brews them!

I saw one of those on TV, I want one!