Does co2 continuously drop or is it just a daily thing? - The Planted Tank Forum
 
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post #1 of 13 (permalink) Old 04-13-2005, 02:34 PM Thread Starter
 
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Does co2 continuously drop or is it just a daily thing?

I put in a hagen co2 unit w/ladder on Sunday, before adding the co2 my ph was 7.0. Monday I didn't have time to test and last night I tested and it was 6.6, I just tested (lights on maybe 1hr) and it reads 6.4.

I know that ph will drop with the addition of co2 but what I'm wondering is>

Is this going to be a slow constant decline (because it's a new system) OR is this just a day/night swing? Should I be able to tell if this is a day/night by testing periodically today and seeing if 6.4 is maintained?

I realize that until I have several tests to evaluate this I won't know for sure but I was just wondering at what point (days...?) does the ph stabilize somewhat after the inception of co2?

The fish all look fine, no gasping so I'm also wondering if I should add an airstone or just wait it out and see?
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post #2 of 13 (permalink) Old 04-13-2005, 03:24 PM
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Regular testing of pH is the best way to tell what is happening with regards to CO2 in your tank.

It's hard to guess how low your pH will eventually get..... it depends on your KH value (buffering ability), CO2 loss at surface, CO2 use by Submerged Aquatic Macrophytes (SAM's), bubble rate etc.

Testing before the lights go on will tell you how much you have available for SAM's.
Testing just before/at lights out will tell you how much the SAM's have used during the day.
Testing during lights on (throughout the day) will tell you even more about your CO2 levels, but is probably unnecessary.
Testing during the night will tell you either; a) how much CO2 is building up when SAM's aren't using any (if you leave CO2 on), or b) the rate at which CO2 drops if you turn it off overnight.

I invested in a pocket pH meter which allows me to test whenever I like without having to spend time and a lot of money on liquid test kits!
A permanent pH meter (in-tank probe) is another (more expensive) option to be able to monitor pH constantly.

I would test day and night (before lights come on / just after lights go out) to monitor levels.


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post #3 of 13 (permalink) Old 04-13-2005, 04:06 PM Thread Starter
 
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That was great thx I'll test the two 2x/day and see how things turn out. In the meantime would you use an airstone at night with that drop? The fish seem fine and swimming (not gasping).
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post #4 of 13 (permalink) Old 04-13-2005, 04:30 PM
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A potential problem area which Stu hinted at is your KH level. If you KH level is < 3, you could get into a pH crash situation which can cause massive fish die off. If your KH > 3, then you should have enough buffering capacity to keep pH levels in a safe range.

Note, I didn't say where KH=3 feel, because I don't recall what others have recommended. I'm up at KH>=7, so it's never been an issue in my tank.
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post #5 of 13 (permalink) Old 04-13-2005, 06:04 PM
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Quote:
Originally Posted by cake fan
In the meantime would you use an airstone at night with that drop? The fish seem fine and swimming (not gasping).
Personally, I wouldn't worry about a change in pH of 6.6 to 6.4. I see a 0.2 fluctuation in my pH readings over the course of the day/night myself.

Apart from perhaps a few hyper-sensitive species (I doubt it), a change in pH of 0.2 is not harmful, and most fish species would probably see a change of much more than this in a daily cycle in their natural habitat if it contains submerged plants.

As for running an airstone, and nighttime worries.... the decision is more dependant on CO2 levels, which is calculated from the pH value, not the pH itself.
Say you did have a KH of 3 (as example only), a pH of 6.6 = 23ppm CO2, and a pH of 6.4 = 36ppm CO2. 36ppm is good IMO, and therefore you would not need an airstone running to outgas some excess CO2.
It all depends on what level of CO2 you are shooting for really, then you can fine tune your system to maintain it.


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post #6 of 13 (permalink) Old 04-14-2005, 12:51 AM Thread Starter
 
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My kh is 2 so then I guess I'm ok without!?
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post #7 of 13 (permalink) Old 04-14-2005, 01:27 AM
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Cake Fan:

I would raise the KH with baking soda and reference this chart:

https://www.plantedtank.net/forums/sh...ad.php?t=14103

to find you CO2 level in ppm. With pressurized a good level is 30ppm. With DIY you might have problems maintaining this though. I would recommend using two bottles and recharging every other to keep the system constant.

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post #8 of 13 (permalink) Old 04-14-2005, 02:15 PM Thread Starter
 
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If I increase the kh then it would bring me to the yellow range which says that it's dangerous for fish. I don't mean to question you but I have to ask if raising it would hurt the fishies? I seem to be at the high end of the good range, isn't this sufficient for plants?
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post #9 of 13 (permalink) Old 04-14-2005, 02:32 PM
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If you raise your KH then you will also increase your pH without a concommitant raise in your CO2 level. The chart is basically saying if your KH is this value AND your pH is this value then the CO2 level is this value.

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post #10 of 13 (permalink) Old 04-14-2005, 03:05 PM
 
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Just to clarify Brian's correct response: if you increase Kh a little, pH is also going to increase a little, and your CO2 level will remain constant...or in fact it might go down just a little. This is because the increase in Kh will allow the water to buffer changes to pH a little more effectively. You might see a 5ppm decrease in CO2 if you raise Kh by 1 degree.
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post #11 of 13 (permalink) Old 04-14-2005, 03:26 PM Thread Starter
 
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I understand that raising one will subsequently raise the other(s) but my concern is that right now my readings are:

nightly readings > 6.4 ph kh2 >>24ppm
daily readings > 6.6 ph kh2 >> 15ppm

I see the daily readings are low but both according to the chart are in the green range (good) and if I up the ph/kh by .5 then my readings will be in the yellow range, which says, they are dangerous for fish.

Also all I'd want to raise it is .5 (to 2.5kh from 2.0) does raising it such a low number really make that much of a difference for the plants and is it worth risking the health of the fish?

It seems like a lot fiddling with the parameters for .5, now if it's worth it and won't injure the fish I'll do it but it just seems like a lot of effort for such a small difference that could affect the livestock detrimentally.
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post #12 of 13 (permalink) Old 04-14-2005, 07:29 PM
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I can see no way that a .5 rise in KH would have any detrimental effect on your fish. I would also suggest that you try to get your KH above 3 as a minimum to keep from having a pH crash, especially with a fermentation generator for your CO2. They are just not as predictable as pressurized and I wouldn't risk it. For example you could double your KH (4) and leave the pH at 6.8 (a better pH for the fish than 6.4 IMO) and still have 19ppm of CO2. Or you could increase the KH to 5 and keep the pH at 6.8 and have 24ppm CO2 (better for your plants and should have no ill effect on the fish). Plus the extra buffering capacity that you would have will give you a little bit more wiggle room. Thats my two cents.

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post #13 of 13 (permalink) Old 04-14-2005, 08:28 PM Thread Starter
 
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Very good explanation, thank you. I know the premise for raising kh/ph but I've never had to actually do it. According to this calculator on my 10gal tank (2kh)
http://dataguru.org/misc/aquarium/calKH.asp

I'd have to use .58 tsp of b.s. would everyone agree? This would also have to be spread across a few days (.4 per day).

I've never had to raise my kh/ph before so any advise/experiences would be appreciated and welcomed
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