Fluctuating PH with auto CO2 - Help!?! - The Planted Tank Forum
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post #1 of 23 (permalink) Old 01-31-2010, 05:36 PM Thread Starter
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Fluctuating PH with auto CO2 - Help!?!

Ok, so here is my situation. The main problem is that my PH is fluctuating by around .3 . Sorry if I am long winded. I have an automated CO2 set up with a Milwaukee controller. The set point is set for 6.5 and CO2 is pumping out like crazy (maybe 4-5 bubbles per second....I set it this way). My drop checker indicator has historically shown that I do not have enough CO2 dissolved in the water, but yesterday I had the ideal mix.

Now, based on the appearance of my tank and plants, everything looks great! I have a full carpet of glosso, a thick jungle of Bacopa and Lugwigia, medium swords, spreading hair grass, and a few others. Plus all the plants are bubbling off lots of oxygen! This is great huh!

Well, the reason for my concern is that on Tuesday I will be getting 6 half dollar sized discus from a local hobbyist breeder and adding them to my tank (yes, a planted tank is not a big enough challenge...I am going to up the ante and attempt to grow out discus in the planted tank!). So, as you might imagine, the fluctuations in Ph concern me...I don't want the fish to die. Currently, I have two flying foxes and a couple of ottos and they have been doing just fine (but they of course are not Discus!).

So, back to the PH fluctuations, my tank has an overflow and a homemade trickle filter. I imagine that I off gas a good bit of CO2, but I have raised the overflow pipe and sponge, added 3 sponge walls around the interior of the over flow to slow the "water fall" effect, I have covered both the over flow and trickle filter with plastic wrap. I cannot think of any other way to minimize the off gassing with this tank (oh, and I do have a DIY Rex Grigg style reactor).

For a while there, the tank was not putting out enough actual CO2 bubbles...the controller was working well I guess. It kept the PH at 6.5, but I still wasn't getting the amount of dissolved CO2 that my plants needed. Then I discovered the relationship of Kh to PH to CO2! Aa-ha! My water consequently is very soft. So, I figured that I would need to "trick" the PH controller by adding baking soda to the tank and raise the KH/PH, and therefore the controller would then open up the "flood gates" so to speak, and release a lot more CO2 in order to drop the PH back down to 6.5 (PH only went up to maybe 6.8). All of this has happened in the last week. But now, I have noticed that the PH is still fluctuating and the CO2 gass is pumping out like crazy and the hardness is lower. Why isn't the CO2 dropping the PH back down to its set point?

My tank is 75 gallons. I took measurements this morning of both my aged tap water and current tank water. Here are the parameters:

Aged Tap: Tank:
PH - 7.5 PH - 6.7 (why not 6.5 as set?)
Nitrate - 12.5 Nitrate - 12.5
Nitrite - <.3 Nitrite - <.3
Ammonia - 0 Ammonia - 0
GH - 2 GH - 3
KH - 2 KH - 3.5/4
Phosphat - 1 phosphat - >2 (probably pretty high)
Iron - 0 (need to dose!)

Let me know your thoughts, I would greatly appreciate any advise! I will upload pics soon hopefully.

Thanks,

- John
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post #2 of 23 (permalink) Old 01-31-2010, 05:45 PM Thread Starter
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Sorry for the formatting mistake w/ the water parameters. Here it is again:

Aged Tap:
PH - 7.5
Nitrate - 12.5
Nitrite - <.3
Ammonia - 0
GH - 2
KH - 2
Phosphat - 1

Tank:
PH: 6.7
Nitrate - 12.5
Nitrite - <.3
Ammonia - 0
GH - 3
KH - 3.5/4
Phosphate ->2
CO2 - 23? 17?
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post #3 of 23 (permalink) Old 01-31-2010, 06:51 PM
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CO2 induced pH swings are not equal to standard pH swings. You could have a CO2 induced swing of greater that 1 point and you would notice no effect on fish. The effect comes from overdosing CO2. With that if you have a pre CO2 pH of 7.5, don't expect your discuss to adapt like it is actually a tap of 6.7 despite the readings you are getting.
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post #4 of 23 (permalink) Old 01-31-2010, 08:25 PM Thread Starter
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Should I plug the controller into my timer so that it stops all CO2 at night, or just leave it going all the time?
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post #5 of 23 (permalink) Old 01-31-2010, 08:43 PM
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Completely up to you. I always injected 24/7(didn't use a controller either). Hypothetically your controller should minimize how much is used at night since plants won't use any co2.
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post #6 of 23 (permalink) Old 02-01-2010, 12:44 AM
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While you can run CO2 24/7 there is absolutely no reason to and if I had sensitive fish like discus in my tank I would definitely make sure it was off at night. The plants don't need it then and the fish certainly don't either.

I don't use a ph controller (don't think it is necessary) but if I did I would leave it shut off until I had my CO2 level dialed in and found it to be consistent over the course of a few days. Then I would check the pH of the tank (once the water is saturated with CO2) and set the controller accordingly. Then if the controller didn't keep the CO2 levels where they needed to be I would toss it. As already noted the pH swing from CO2 is not harmful to your fish. What is harmful is too much CO2 so make your adjustments slowly. Raise levels over the course of a few days and never increase bubble rate if you are not going to be home to watch the tank.

You should not have any nitrites in the tank if it is cycled. If your test kit is accurate it is not a good sign that you are getting a reading. Make sure nitrites are zero before adding the discus. FWIW the commercial iron test kits are useless so don't worry about your iron reading zero. You should be dosing micros with a trace mix like Flourish comprehensive or the dry CSM+B. Both of those contain enough iron for most tanks.
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post #7 of 23 (permalink) Old 02-01-2010, 12:50 AM Thread Starter
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Doesn't dosing macros add nitrites to the tank?
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post #8 of 23 (permalink) Old 02-01-2010, 12:56 AM
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No, dosing macros only adds nitrates, not nitrites. Nitrates are what the plants need for food.

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post #9 of 23 (permalink) Old 02-01-2010, 02:41 AM
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I vote for shutting off CO2 at night too. pH swing is ok every day BUT too much CO2 can kill your fish (that's where a controller is handy). As said before as much as a 1 point swing can be ok. Watch livestock closely!


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post #10 of 23 (permalink) Old 02-01-2010, 03:46 AM
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Using a PH controller like the OP is already would mean that the co2 really won't get injected at night, since co2 is only being lost at the surface, not taken by plants. No need to turn it off, if that is the case.
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post #11 of 23 (permalink) Old 02-01-2010, 10:27 AM
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Quote:
Originally Posted by over_stocked View Post
Using a PH controller like the OP is already would mean that the co2 really won't get injected at night, since co2 is only being lost at the surface, not taken by plants. No need to turn it off, if that is the case.
To get an adequate amount of CO2 you need to set the controller from .5 to 1.0 point below the natural pH of the tank eg: tank minus any CO2 is 7.3---you set controller for, say 6.5. That will give you somewhere in the vicinity of 30 ppm CO2. BUT you don't need that at night AND if you don't shut off the solenoid with a timer you will have CO2 running all night long to keep tank at 6.5. The idea of using the controller is so you can set a high bubble rate to get the tank enriched with CO2 when the lights come on (CO2 comes on one hour before lights on). But the higher rate could be dangerous to fish hence the safety measure of the controller shutting off CO2 when the target pH is reached. You absolutely do not need CO2 injected at night-you're wasting it and stressing the livestock.


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post #12 of 23 (permalink) Old 02-01-2010, 01:46 PM
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Quote:
Originally Posted by over_stocked View Post
Using a PH controller like the OP is already would mean that the co2 really won't get injected at night, since co2 is only being lost at the surface, not taken by plants. No need to turn it off, if that is the case.
Except that you do lose a significant amount of co2 at the surface.


However, it's totally up to you. I prefer to shut off co2 at night. There's no need for it, and shutting off co2 at night will make the cylinder last twice as long(actually, longer since you'll probably only have it running for 10 hours, not 12).


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post #13 of 23 (permalink) Old 02-01-2010, 03:40 PM
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As always great info in the replies with many options and opinions.

OP, my understanding is to set your water (species specific) parameters regarding KH/pH before introducing the CO2.
Meaning if you want 7pH for your fish then base your water chemistry for 7 then drive it down to between 6 and 6.5pH for water column CO2 content. What your fish are living in is the mineral content of the outgassed water.

I supply two 75g tanks off one 20lb cylinder and SuMo regulator. I've chosen the controller method as well using American Marine units. I do not aerate at all. Both tanks are maintained at or near 35ppm CO2 24/7. On the rare night I can't sleep I can tell you the controllers do not activate or do only once at late hours for a short period. The tanks are both fully stocked. Only once after a heavy pruning have I seen any 'gasping' in the tanks.

Also the current cylinder was placed in service July 2008 , so it has supplied my needs for over a year without the high pressure gauge moving off 900lbs. (accept following ambient room temperature)


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post #14 of 23 (permalink) Old 02-01-2010, 03:49 PM
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Quote:
Originally Posted by wkndracer View Post

OP, my understanding is to set your water (species specific) parameters regarding KH/pH before introducing the CO2.
Meaning if you want 7pH for your fish then base your water chemistry for 7 then drive it down to between 6 and 6.5pH for water column CO2 content. What your fish are living in is the mineral content of the outgassed water.
This isn't actually necessary. You can use whatever source water you'd like. If it's healthy for you fish to live in without injected CO2, it'll be healthy for your fish to live in with injected CO2. The exact pH drop changes based on different water chemistry, so it's good to have a drop checker around with 4 dKH solution in it to find your ideal pH.


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post #15 of 23 (permalink) Old 02-01-2010, 06:30 PM
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"This isn't actually necessary. You can use whatever source water you'd like."

OP's original post questions pH swing and the keeping of discus. My choice of soft water species required the use of RO to achieve results I'm happy with. Happy for me as defined by fish constantly breeding. People state domestic angels can be kept in a broad range of GH, KH, pH successfully. True but define your success. I never had a spawn survive until I softened my water (I am aware that others do). I've kept various strains for years but until I reduced my water hardness next to no spawning activities. With discus targeted as a primary display species most folks posting parameters maintain soft water conditions with very few exceptions. I do understand that GH and pH are unrelated but in normal terms low GH and low KH generally go together and make water changes easier. My experience is all I can share and that is with <6dGH, <3dKH less health issues with live stock along with very healthy plants.
I maintain tanks with >9dGH so I can keep briggs and other snails. There are angels in these tanks also and they do not spawn repeatedly as the others do in the soft water tanks.

There's a vendor in Texas breeding and selling discus raised in higher mineral content water but to date he's the only one I've seen.

I thought I mentioned earlier also that the OP posted a .3 swing in pH which is quite small. I have a spare controller installed on a low tech non injected system that swings nearly a full degree in pH reading during the day.


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