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CO2/pH level in planted tank

M

Marcel G

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Has anyone measured pH level during 24h interval in his planted tank?
I would like to know if pH/CO2 is continually increasing during the day, and begin to decrease only after lights are off ... or if it increases after turning the lights on until it reaches some level, and then stays constant/stable during the rest of the photoperiod? Has anyone measured this?

CO2_pH_level.jpg


Marcel
 
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Would be interesting to see the answer to this. I measured mine the other day out of curiosity and it was pretty much constant right throughout the lighting period. I measured again the next morning before I left for work and it was still the same even before the co2 had switched on. I put this down to left over co2 levels from the dark period and possibly that the co2 I'm injecting is getting used in the lighting period. Would be interesting to see if the ph should raise at some point.
 

Martin cape

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Mine dips down from about 7 to 6.3 in the first 2 hours co2 is injected. Then stays the same for the entire lighting period. It must go back up to 7 ish during the night.
 
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Now you have me worried!
 

plantbrain

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Generally a pH drop of 1.0 will yield about 30 ppm.
1.2: 45 ppm
1.4: 70 ppm.

As you go higher, the change in pH adds a lot more CO2 than at the lower ppm ranges.
So you need finer adjustments and to be more careful the higher concentrations you add.
 
M

Marcel G

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Thread starter
Hi Tom (plantbrain),

how is it possible to get at the first option (graph) without pH controller? I'm now tracking my 60L (15G) tanks, where I use DIY CO2 reactor according to your design. The dissolved CO2 is distributed by spraybars. What should one do to reach the highest possible (= stable/constant) CO2 level as soon as possible without pH controller? How do you do that? I add dissolved CO2 (so no escapes to the air), have plenty of plants ... but still my pH seems to slowly increase throughout the whole photoperiod (from 7.5 to 6.4).

Marcel
 

tubamanandy

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Ok, currently my 56 litre tank (KH 5.5) sits at PH 7.34, when lights come on & CO2 (gas) is fed into the reactor, PH only drops to around 7.21 slowly over the next 7 hours with addition of around 1 bubble/second.

With a KH of 5.5 I guess I would need to be adding alot of CO2 to get the PH below 7.0 ?

Thinking of dropping the KH to around 3-4 so I can get PH a little lower - am I making sense ?
 

Simanas

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9 Nov 2009
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Dropping KH wont increase CO2 concentration in water, so I dont know why would you need to decrease KH.
 

tubamanandy

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I was wanting to drop KH slightly so I would be using less gas and have the flexibility that, if I increased the bubble rate of CO2 the PH could be dragged down a bit further.

I maybe wrong in thinking this.
 
M

Marcel G

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Thread starter
The CO2 concentration in your tank is around 7-10 mg/L. If you want more, just increase your buble rate. BTW I have similar KH in my 60L tank, and I use 3 bps. My default pH read 7.5 (before lights on), and my peak pH value reads 6.4 (before lights off). If you have any further questions, please, create a new post on this subject. Here we are tracking CO2 levels during 24h interval + how to reach constant/stable level.
 

Simanas

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Hi Tom (plantbrain),

how is it possible to get at the first option (graph) without pH controller? I'm now tracking my 60L (15G) tanks, where I use DIY CO2 reactor according to your design. The dissolved CO2 is distributed by spraybars. What should one do to reach the highest possible (= stable/constant) CO2 level as soon as possible without pH controller? How do you do that? I add dissolved CO2 (so no escapes to the air), have plenty of plants ... but still my pH seems to slowly increase throughout the whole photoperiod (from 7.5 to 6.4).

Marcel

I think aeration plays major role in stabilizing co2. Check this testing: Stable enough CO2? - Aquarium Plants
 
M

Marcel G

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Thread starter
Hi Simanas,
this is exactly what I have found a few minutes ago :) . According to the graphes it really seems that due to aeration the CO2 level stabilizes:

CO2 without aeration (with siesta):
11103003bpsnoaeration.png


CO2 with strong aeration:
1110301bpsviolentaerati.png


On the other hand, Tom Barr (plantbrain) doesn't use aeration in his tanks, but uses wet-dry filters (which could play a similar role as aeration). That's the reason I asked him what is the reason of his constant/stable CO2 level throughout the photoperiod.

Maybe it could help a lot, if we have the CO2 on for 24/7. That way it could build up to the highest level, and stay there for 24/7. But in this case we need to add smaller amount of CO2, because there will be practically no degassing at night (or due to aeration), and therefore no rest for fish.

What do you think about it?
 
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How come?

My KH is generally 5, Using a standard bromo blue kit my PH is 6.4 all day long long right throughout the photo period. I do have a ph pen but I can't trust it. When I had a break from fishkeeping for a couple of years it was left without storage fluid in a cupboard and I have no calibration fluids. Looks like it's time to have an investment and look a bit deeper into the whole co2 situation.
 
M

Marcel G

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#17: What are you doing for your pH to stay at the same level during whole photoperiod? Are you using aeration in your tank, or do you use wet-dry filter, or do you add CO2 for 24/7?
 
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Not sure why my ph stays the same. Co2 is on 3 hours before lights and 3 hours before lights off. I don't aerate the tank but I do have a Koralia that causes a very slight disturbance of the water surface. I do this because the tank is quite heavily stocked. Confuses me a bit with the ph being constant because it's constant at 6.4, in theory that means with a kh of 5 there should be plenty co2 in the tank unless something else is acidifying the water. It comes out the tap at 7-7.2
I've recently started work on a journal so all would probably be clearer from that.
 

plantbrain

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Hi Tom (plantbrain),

how is it possible to get at the first option (graph) without pH controller? I'm now tracking my 60L (15G) tanks, where I use DIY CO2 reactor according to your design. The dissolved CO2 is distributed by spraybars. What should one do to reach the highest possible (= stable/constant) CO2 level as soon as possible without pH controller? How do you do that? I add dissolved CO2 (so no escapes to the air), have plenty of plants ... but still my pH seems to slowly increase throughout the whole photoperiod (from 7.5 to 6.4).

Marcel

Because the rate of degassing is relatively constant. It goes up and then levels off. Same with the levels of CO2 that build up inside a bag you breath into.
With relatively accurate CO2 dosing, you should be able to add more and more CO2 and have it flatten at some equilibrium. Each time the RATE of CO2 addition increases, there's a time delay which is based on the flux of CO2 leaving the system. This controls the level.

It's a 2 box model if you want to keep it simpler. What goes in, must come out.
1. If you suddenly had surface film form on your tank, the graph shape would change. How would you predict the shape change if that occurred?
2. What would happen if the out put pressure on your regulator went from 15 psi to 9 psi?
3. What would happen if the powerhead for additional flow was stopped?

The constant for degassing will not change in Fick's 1st law, but the distance might(surface films etc), rate of exchange, the surface area(turbulence) and concentration differences. .
 

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