C0 2 for pH control

[Heliman]

My set up (1000 litres, mixed reef, mainly SPS) has been in operation for 8 months now.

I am really happy with how it is all going, I dont have any problems to speak of !!

All key parameters are under reasonably tight control and dosing automatically takes care of Ca, Kh and Mg (460, 8.5 and 1350 respectively)

Po4 is at 0.02 and No3 always 1 or 2 ppm.

No nuisance algae or cyano.

As is normal , now I have a fairly high bio-load, I am experiencing a day/night pH swing...from 8.20 at lights on, to 8.41 at lights off. This is, I believe a function of CO2 generation by the bio-load during the day (minimum) due to photosynthesis and tending to maximum in the dark hours for the same photosynthetic activity going into reverse. As the Tank is in it's own room, fed by outside air and not influenced by what/who is present in my home, I am sure that the "local" environment and CO2 retention is not an issue. I have heavy water movement (48 turnovers/hr approx), good surface agitation and run a large skimmer 24/7 !!

I suspect that this type of pH swing is not abnormal, but it is the only parameter I have that exhibits such daily changes and I would like to get it a bit more stable. The Ocean does not experience such large swings and in some ways I feel SPS might be a bit happier in a more stable pH environment ??

I am considering using CO2 injection with a pH controller to better manage the drift to alkalinity during daylight hours.

Can anybody give me some advice/pointers as to how or if this methodology might or might not work, based on any real time experience you might have.

 

[alexander_ktn]

I personally find your pH variation absolutely acceptable and quite small, but if you want to counter it I'd rather recommend a reverse lighting cycle algae refugium. You might spur algae growth with adding CO2 to your tank when the lights are on.

I furthermore think it's an unnecessary potential point of failure - imagine your pH probe/controller malfunctioning...

I once had a kalkwasser stirrer not stopping (I also used it with a pH controller and it malfunctioned) and woke up to a tank with a pH of 8.6 and rising... Had I not been there my fish/corals would probably have been lost.

 

[disc1]

The Ocean does not experience such large swings

Sure it does. In many places on the natural reef the swing is much greater than that. Two tenths of a pH unit is almost nothing.

 

[daido]

No!!!! Do not use co2 to balance the ph. What would happen if something with high ph will get into the water? A ph of more than 8.6 can cause the system to add in lots of co2 which will lower the amont of of oxygen which causes bad things to happen. Dose alk at night and that is it.

 

[JPMagyar]

I third the motion of not using CO2 alone, I would, however, consider adding a calcium reactor which will undoubtedly lower your pH.


Joe :beer:

 

[disc1]

No!!!! Do not use co2 to balance the ph. What would happen if something with high ph will get into the water? A ph of more than 8.6 can cause the system to add in lots of co2 which will lower the amont of of oxygen which causes bad things to happen. Dose alk at night and that is it.

How does adding CO2 cause oxygen to disappear? That isn't how it works. You can have a high level of both or a low level of both. They're not hung into any sort of inversely proportional relationship except in the one case of respiration/photosynthesis. But just adding one isn't going to do anything to the concentration of the other.

 

[Brummie]

I've used CO2 to increase algae growth on my scrubber. It does a grand job of lowering the pH and increasing the mass of the scrubber algae but as already mentioned, it's not without it's concerns. I found growth of heterotrophic dino's the main problem, blocking pipes up etc. Not sure why Co2 would cause this (I've put it down to an excessive production of exudate from the scrubber). Gone back to normal inside air now.