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CO2 tuning and pH profiling

MMonis

Member
Thread starter
Joined
19 Mar 2021
Messages
70
Location
Aalborg, Denmark
Hey folks,

I have been reading a bit about CO2 and how to tune it to ensure an optimal level in the tank. I am using a Hanna pH meter for pH testing and CO2 drop checker with 4dkh solution.
Tank parameters are:
Size : 54 litres (60 cm x 30cm x 30cm)
Filter: Oase Biomaster 250 with output as a spray bar
Co2 diffusion: CO2art inline diffuser and starts 2 hrs before lights on @2.3 bps
Light: Fluval Aquasky configured at 63% intensity. Lights on for 6 hrs

Based on my water report from the water company, values are:
Total hardness GH: 14° dH
Carbonate hardness KH: 9.7° dH
pH : 7.4 (I also verified the pH with the pH tester and it was indeed 7.4)

Now if I take water from the aquarium and measure the pH after degassing for 24 hours it reads as 8.3. Is it common that there is almost a 0.9 pH difference between the tap water pH and the degassed water pH from aquarium ? Also if I leave it for more than 30 hours and measure, then the pH shows slightly higher than 8.3. Is there a time period for which we need to consider as degassed water ?

If I then run a pH profile with a bubble count of approx 2.3 bps, here are the results
TimepHActivity/RemarksDrop checker color
13:007.9seems like residual co2 existsBlue
14:007.9CO2 ONBlue
15:007.2Blueish green
16:007.0Lights ONslight greenish
17:006.9green
18:006.9green
19:006.9greenish yellow
20:006.9greenish yellow
21:006.9CO2 OFFgreenish yellow
22:007.2Lights OFFlight green

Should I take the 1 pH drop from degassed pH (8.3) or the pH just before CO2 is started (7.9) ?

I haven't measured the kH of the aquarium water, but if I use the kH value from the tap water and fill the values in the Rotala calculator it says that the target pH should be 6.9. Is this correct ?
1651169145554.png

Does one need to measure kH of the aquarium water to arrive at the correct pH drop values when injecting CO2?
Is 2.3 bps a bit too much since it drops the pH by 0.7 (7.9 - 7.2) in the first hour itself and then the subsequent pH drops are much smaller.

Regards,
Mel
 

MMonis

Member
Thread starter
Joined
19 Mar 2021
Messages
70
Location
Aalborg, Denmark
I now started pH profiling with the degassed water pH being 8.3 with bubble count as approx. 1.66 bps
TimepHActivity/Remarks
24hrs degassed8.3
11:307.9CO2 ON. Residual co2 causing pH of 7.9 in tank
13:307.4
14:307.3Lights ON
15:307.2
16:307.2
17:307.2
19:307.1CO2 OFF
20:307.4Lights OFF

At the rate of injection of 1.66 bps it takes roughly 3 hours for a 1 pH drop. Should i increase the injection rate to see if the 1pH drop can be achieved faster ?
 

Zeus.

Fertz Calc Meister
Joined
1 Oct 2016
Messages
4,602
Location
Yorkshire,UK
At the rate of injection of 1.66 bps it takes roughly 3 hours for a 1 pH drop. Should i increase the injection rate to see if the 1pH drop can be achieved faster ?
NO !!!! - classic mistake/error, once the pH is stable from lights on till CO2 off then the time it takes to get the pH drop is the time it takes - unless you have twin solenoids, timers and CO2 injection
Your pH drops 0.2pH from lights on till CO2 off, which isnt bad at all but 0.1pH drop for same period would be better. To achieve a more stable pH/[CO2] decrease the BPS slightly. check again and if happy just time it takes to get the pH drop.
Sorry, I missed your first post on Thursday. I have only ever tested my KH once and ignored its valve as like you I have hard water. KH is hard to measure accurately and KH is really alkalinity and measuring to get a pH to aim for a target pH to get 30ppm CO2 is prone to errors. Accept you have enough KH forget the value and move on is my advise.
Good job doing the pH profile :clap:
 

Yugang

Member
Joined
13 Mar 2021
Messages
391
Location
Hong Kong
Your profile does not look bad. Observing the relatively long ramp up time, as well as residual CO2 before starting to inject, may indicate that your surface agitation (and thus CO2 outgassing at water surface) is relatively low.

If, despite already reasonable profile, you chose to further optimise then you may increase surface agitation. This would require higher injection as well, but enables steeper ramp up, and improved stability during lights on.

The following link may be helpful
 
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