ph Persistence with CO2 and Water Changes

[SwampeastMike]

How quickly does the ph fluctuate when using CO2 fertilization systems?

How long after the system stops until ph rises to "normal"? hours? days? weeks?

If target ph is 6.7 with tap water ph 7.6 (5 Kh, 8 Gh) mixed with rainwater does a large water change stress the fish who can tolerate such but prefer lower?

 

[Caliban07]

How quickly does the ph fluctuate when using CO2 fertilization systems?



How long after the system stops until ph rises to "normal"? hours? days? weeks?



If target ph is 6.7 with tap water ph 7.6 (5 Kh, 8 Gh) mixed with rainwater does a large water change stress the fish who can tolerate such but prefer lower?

How much or quickly the pH drops depends on many things.

If you have a high injection rate and poor aeration then the curve will be steep. If you have a high carbonate hardness the more the water will resist pH change. Lots of plants and higher light levels will also increase uptake of the co2 you inject etc.

It will stabilise faster based on these elements too.

I don’t think the water change will stress the fish.

 

[SwampeastMike]

Thank you.

Since it can cause asphyxiation symptoms in fish at night when both they and the plants are producing CO2 it must be quite transient with, ideally, the carbonic acid existing only to replace the CO2 being consumed by the plants. In such case the water tests more like acid than it works like one, correct?

Not planning a CO2 system immediately.

Doing further research to find it seems best to maximize the natural CO2 via aeration and reasonable bio load then experiment with lighting time and intensity in attempt to maintain proper growth with minimal algae and no enrichment.

 

[Caliban07]

Perhaps have a look at this article.

https://www.2hraquarist.com/blogs/choosing-co2-why/how-to-push-the-limits-of-co2-safely

There is no substitute for oxygenation, even if that means increasing the co2 somewhat.

pH can swing very wildly in natural waters. Taken from Walstad’s Ecology of the Planted Aquarium

‘Daily variations of the water parameters are rarely – if ever – taken into account. Data collected in a freshwater lake (Star Lake, VT) with a very low alkalinity showed a diurnal pH fluctuation beyond the imagination of most hobbyists. Thus, the pH at 10 am was measured at 5.7 (strongly acidic), 9.6 at noon (strongly alkaline), 8.3 at 2 pm (moderately alkaline) and finally, 6.4 at 4 pm (slightly / moderately acidic). Readings were taken at a 0.5M depth. The fluctuation observed was due to the low KH value of the water (something reported for the Amazon river, too) and the presence of large amounts of phytoplankton. Under the circumstance it is extremely difficult, if not impossible, to figure what is the “right” pH for any form of aquatic life collected in that lake and which tank could cope with this kind of fluctuation. The low – high points of the day differ by 4 pH points, which means that the concentration of H+ in the morning is 10.000 times higher than at noon, while this change takes place in just two hours. It goes without saying that this pH swing cannot be observed in an aquarium only because we cannot reproduce the amount of light which falls in the Lake. In any case, if somebody reported that a suitable pH for aquatic life collected in this lake should range daily from 5.7 – 9.6 most hobbyists would think it was a typo’

 

[Delapool]

On mine I would say the ph returns to normal (from CO2 injection stopping) within several hours in morning and then does it all again in the afternoon.

The ph probe controller is turned off (and on) using a timer so generally I don’t get to see ph lifting back up so bit of guesswork here.

Main issue I’ve found is over-dosing CO2 and bumping off fish. They’ll happily take food anytime when CO2 is running.

 

[SwampeastMike]

Would be much better and more practical if ph was the only thing that changes when you force water to accept more CO2 than it wants and try to keep it in the water.

Water circulation of the sort that works to fully gasify the water requires additional CO2 that forces out yet more O2.

Creatures come first in the 160-gallon tank I'm working on.

 

[Caliban07]

Would be much better and more practical if ph was the only thing that changes when you force water to accept more CO2 than it wants and try to keep it in the water.

Water circulation of the sort that works to fully gasify the water requires additional CO2 that forces out yet more O2.

Creatures come first in the 160-gallon tank I'm working on.

This is why I no longer use co2. Snails and shrimp don’t like it.

Not quite sure what you mean in the middle paragraph?

 

[Delapool]

Found the same on snails.

Fish mainly seem to do fine. I found they got lethargic if too much CO2 (rather than going to surface or something). Lost a couple at start and all good now. Ph / CO2 kit is well past use by date but still works ok.

 

[SwampeastMike]

Not quite sure what you mean in the middle paragraph?

See Paragraph 4.1

CHEMICAL FEATURES OF WATER

When CO2 "bubbles up" it "washes" dissolved oxygen from the water. Further agitate the surface and it happens even more quickly.

 

[skywhitney]

I never had any issues with snails and shrimp, quite the opposite actually, when I ran my CO2 system. I always kept the PH controller in the 6.3-6.5 range. I never did water changes though, only top offs when needed so my parameter swings were always minimal.