A word of caution to those using CO2 scrubbers!!

[MnFish1]

I can confirm that what @Pete_the_Puma said is absolutely true and confused by why you are saying a CO2 scrubber will reduce alk demand above which isn't true. My tank consumes a considerable amount more alk with the scrubber than without to the point that I absolutely will get an alk spike (if no change to dosing is made while media is left exhausted) as he describes if I don't replace the media to maintain ph before its exhausted.

CO2 scrubbers can absolutely have a BIG impact on PH and thus alk demand. My core 7 dose is about 20 ml different with and without a scrubber for reference.

I'll repeat it again - if one has a piece of equipment on a tank - that is designed to do something - like this - i.e. remove CO2 - leading to a higher pH - and thus (moderate - or minimally) higher coral growth and thus alkalinity consumption - its the responsibility of the person to realize the chemistry of that device - and not be surprised when things are off balance if it fails. I would not apply a CO2 scrubber to my tank - unless I realized what it was doing - and what would happen if it failed. In any case - apologies to the OP - it would take a fair bit of time to see any big changes in alkalinity, etc etc - if a Co2 scrubber slowly was exhausted. IMHO - its a nice warning. But - its similar to me posting 'be careful - if your tank evaporates so much that your sump is nearly empty -your return pump might not work'.... Both are true right?

 

[CMO]

Its a degree right? Lets say I dont have a Co2 scrubber. I have the windows open in the spring - in May I close them and turn on the air conditioner - the pH drops some. Alkalinity is a buffer - it is 'designed' to help for these changes'. The pH change does not result in a catastrophe for the tank. Likewise pretend I have no Co2 scrubber - I have had my windows closed all summer with the AC on - and thus - the Co2 is higher. There is no disaster that happens when I open the windows in the fall - instead - the pH minimally changes etc etc. There is a difference in an
'ALK SPIKE' - I.e. - I add 500 cc of concentrated Sodium carbonate solution - and and alkalinity rise.

An alkalinity rise - such as what I described above will not harm coral or anything else. The OP is right one might have to turn down alk dosing - but even without that - its extremely unlikely to cause a major disaster (just like closing windows and opening them) does not.

We focus IMHO too much in this hobby on these very minor issues - when in reality - there are far more problematic issues with alk and Ca - most of which involve overdosing based on erroneous testing. again - My opinion.

That may be the case for you but there are other plausible scenarios such as the follow with my tank.

My daily PH without a CO2 scrubber ranges 7.7-7.9. With a CO2 scrubber my PH runs about 8.15-8.35.

Daily Alk consumption with CO2 scrubber is about 70 ml but only 50 ml without.

When the CO2 media becomes exhausted there is a about a 2-3 day time frame during which the tank will transition from the PH range of 8.15-8.35 to 7.7-7.9. If I leave the media exhausting and maintain dosing 70 mls / day that is now 20 ml per day more than I need to maintain my alk level. This does in fact result in a dangerous alk spike of several points if either dosing is not adjusted or media replaced.

If you have a relatively low alk demand tank you may not see as large of a change in demand but with a packed SPS tank a change in PH of this magnitude can significantly change demand pretty quickly.

I'm not saying the spike will occur in a matter of hours but absolutely over a day or 2 with no change would result in a multiple point change in DKH for my tank which consumes a very high level of alk on a daily basis.

 

[MnFish1]

That may be the case for you but there are other plausible scenarios such as the follow with my tank.

My daily PH without a CO2 scrubber ranges 7.7-7.9. With a CO2 scrubber my PH runs about 8.15-8.35.

Daily Alk consumption with CO2 scrubber is about 70 ml but only 50 ml without.

When the CO2 media becomes exhausted there is a about a 2-3 day time frame during which the tank will transition from the PH range of 8.15-8.35 to 7.7-7.9. If I leave the media exhausting and maintain dosing 70 mls / day that is now 20 ml per day more than I need to maintain my alk level. This does in fact result in a dangerous alk spike of several points if either dosing is not adjusted or media replaced.

If you have a relatively low alk demand tank you may not see as large of a change in demand but with a packed SPS tank a change in PH of this magnitude can significantly change demand pretty quickly.

I'm not saying the spike will occur in a matter of hours but absolutely over a day or 2 with no change would result in a multiple point change in DKH for my tank which consumes a very high level of alk on a daily basis.

Actually - youre right - you might be the exception. But - forget the Co2 scrubber - when you close the windows in the winter and open in the summer - though the pH changes there is little issue with the coral - it happens slowly - as it would when the scrubber material gradually decreases.

BTW - My pH with the windows closed ranges from 7.8-8 and with the windows open 8 - 8.2. So - in reality there is no difference. Yet im not posting a warning that its an issue when you close your windows. Anyone that tests their alk regularly (as recommended) - would know this - and adjust it accordingly.

 

[ClearLife]

I want to thank you for explaining the relationship of these parameters. You helped me understand. My biggest take on this is that as usual, each tanks reaction to changes is unique to some extent. Less carbonic acid in the tank reduces the alk load, but the increase in coral growth could also increase the alk load. They counter act each other. The evidence presented here suggests that the reduction in carbonic acid from less CO2 usually has more of an impact on alk load than the increased coral growth. (unless you have an incredable amount of healthy coral.) . Thus the large number of people that say the CO2 scrubber helped raise their PH. It might also explain why some say it increased their PH dramatically while others say the increase was minimal. I think it depends on how much healthy coral you have. I'm amazed at how good you people are when you put your heads together to help someone out. Again, thanks.

I just reallized that most all of you probably already knew all this, but its an appifiny for me.

 

[Dave Cureton]

Thank you for sharing your experience. My thought on leaving the dead tips or cutting would be to cut them off. I have heard that fragging encourages new growth. Not sure if it's scientific or anecdotal but don't think it would hurt to try at this point. I hope your reef makes a full recovery.