CO2 off or on during the night????Please advise - The Planted Tank Forum
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post #1 of 8 (permalink) Old 01-26-2003, 09:55 PM Thread Starter
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I thought I read from most posts and the reason to get a solenoid is so the CO2 can be shut off during the nite when the plants dont need it.Is shutting it off (with a timer) going to cause a big Ph swing? Should I be leaving the CO2 on day and nite?What gives here.

15gal planted,flourite+volcanite,65 watt pc,whisper 2 filter,5lb CO2 tank and diffuser,flourish .
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post #2 of 8 (permalink) Old 01-27-2003, 04:16 AM
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Fine! Don't believe me! LOL!

Really and truly...the main reason to get a solenoid is to hook it to a pH controller. The controller constantly measures the pH and turns the solenoid on and off to maintain a very constant pH reading - 24 hours a day.

If you are injecting CO2 to a fairly high concentration with a pressurized system, I really, really believe that the plants cannot off-gas enough CO2 at night to prevent a significant pH swing if you turn off the CO2 at night.

I know this because at 45 ppm CO2, I hear my controller turn on the CO2 several times every night when the lights are off. Not as often as when the lights are on, but several times nonetheless.

There is an initial period for about 2 hours after the photoperiod is over that my plants seem to do most of their CO2 releasing. After that, the pH rises slowly as the dissolved CO2 escapes into the air and the controller comes on to lower the pH by replacing CO2. No, the plants don't need it at night. However I keep my CO2 at about 45 ppm, and I like my fish alive. I'm not willing to subject them to a 1.5 to 2.0 or more change in pH every 24 hours.

If you have a pressurized system with no pH controller, I'd suggest you not try to achieve a very high CO2 concentration. Set a bubble rate that gives you 10 or so ppm during the day and let it run like that all the time.

I've run pressuirzed CO2 for over 5 years - I've never had a fish kill - and I'm telling you exactly what I'd do if I were in your place. Borrow an electronic pH meter and watch the swings for yourself in real time.

As for the new fish dying... The ones that contracted ich and died before have caused a population explosion of Trophonts and Tomites (2 forms of ich in the non-attached stages of their life cycle). These organisms currently infest your substrate and water column in large numbers. Only the healthiest of your fish may be able to fight off the large number of parasites.

You're giong to have to either:

a) chuck out all the fish and leave the tank empty for 4 or 5 days until all the free Ich forms die naturally because they can't find a host.


b) treat the whole tank for Ich. Quick-Cure from Wal-Mart (and other places) per the bottle instructions should do the trick.

If you cho\ose a), don't put those fish back in your main tank unless you treat them for Ich in a hospital tank first.

Good Luck!


p.s. It's the pH swings, it's the pH swings, it's the pH swings!
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post #3 of 8 (permalink) Old 01-27-2003, 04:40 AM Thread Starter
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Man have I been mislead.I combed this forum listening to all aspects of the hobby .I just cant believe I bought all this crap and find its wrong.Please go to Florida driftwood website and look under their CO2 systems solenoid.They even show a schematic for using it with a timer OR with a controller.I also read and I thought it might have been Amano that said its ok if you ran CO2 during the night that the Ph wont go that far down but youll save gas by putting on a timer and solenoid.Your telling me this is all bad advice then.Im curious,what controller did you buy and how much more do I have to spend! By the way,I have my CO2 exactly as you mentioned-low at 10ppm just in case you are right because I thought about the worst case scenario ahead of time.Didnt matter though to those new fish.It wasnt the ich that killed them either.I guess Im going to have to prove it to myself and measure the Ph during the night.Man am I pissed!!If this is true lets please put this to rest right on the forum in a anouncement becuasde Im sure many others will fall into this trap.

15gal planted,flourite+volcanite,65 watt pc,whisper 2 filter,5lb CO2 tank and diffuser,flourish .
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post #4 of 8 (permalink) Old 01-27-2003, 04:50 AM
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If you believe Tom Barr and *many* others the pH swing will happen but not bother the fish a whit. It occurs in nature as well.

Unless you have unbuffered water it won't swing more than half a point. No big deal.

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post #5 of 8 (permalink) Old 01-27-2003, 06:19 AM
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Get a pH meter and watch.

It's just like the CO2 chart. It's "Holy Dogma" wisdom that you can reliably determine the CO2 concentration by measuring the KH and pH. The mathematics of exponential functions say otherwise. But the mathematics are ignored because "The Chart" is the "Holy Dogma." Fact is that it is virtually impossible to measure the KH (and in most cases the pH) accurately enough with "match the color" test strips (or 1 drop = 1 degree KH titrators) to get good enough numbers to plug into the formula and get meaningful results. If one reads the discussion on the Krib, the guy that posted "The Chart" over there admits this.

On turning off CO2 at night...

Think about this. If you leave a soda bottle open for 12 hours, it goes flat. The ratio of surface area to volume is a tiny fraction of that in an aquarium. Yes there is a much higher initial concentration of CO2 in soda and it looses CO2 much faster in the beginning because of that. I'm just trying to invoke analytical thinking.

If you turn off the CO2 in an aquarium for 12 hours, the CO2 concentration is going to *approach* that of the air at the end of that period. Don't take my word for it. Try it yourself (with a good CO2 test kit... not "The Chart".)

So figure if you turn off the CO2 at night, you're going to loose a very significant amount of CO2 by 12 hours later. Don't believe me. Test it with a CO2 test kit and see for yourself.

If you want to turn off the CO2 at night -

What either works or doesn't... kills fish or doesn't.... is the difference between what the pH is when the CO2 is on and what the natural buffers in the water "want" the pH to be (i.e. what the pH slowly returns to when you turn off the CO2).

In my opinion, this is the critical information Florida Driftwood, Yamato, et al probably know but fail to state clearly.

Draw the pH down by .5 with CO2 and you can very safely turn off the CO2 at night. Draw the pH down by "lots" more with CO2 and you're asking for trouble if you turn off the CO2 at night. Many will debate what constitutes "lots." I would not subject my fish to an everyday pH fluctuation greater than .5 or so (remembering that pH is a logarithmic scale and a change in pH of +/- 1 changes the acid/alkaline ion balance by a factor of 1000%.) But that's just 1 person's opinion. If we can agree that a "big enough" pH change is, at minimum, stressful to fish... Then why in Heaven's name would one want to "push it to the limit" every day? It would seem prudent to try to minimize all sources of stress to both fish and plants. Seems like common sense.

Now if one claims that pH changes of any size are not stressful to fish, then I suppose that's a Tetra of a different color.

On the other topic...

I thought I remembered you saying in another post that some of your fish got Ich during or after the CO2 spike/pH swing period. If I'm mistaken, chalk it up to early senility.

No, I wasn't saying that the Ich killed your fish directly. The high CO2 spike you had initially and the resulting large swing in pH killed some and weakened others. The Ich was just an opportunist. However, now that Ich has had a chance to flourish breifly in your tank, the water/substrate is most likely full of parasites. The more free-swimmers you have, the more likely it is that even the fairly healthy fish will succomb to Ich. Thus the recommendation to treat the tank for Ich. Fish can have Ich quite seriously with NO external signs on the body. It often attaches to the gills where it's hard or impossible to see.

In summary...

In any event, it's really no skin off my nose if I'm believed or not. Many people have been very helpful to me here, including you. I just want to return the favor and try to help with some advice that I honestly believe will help make your problems go away.

You CAN make your current setup helpful to your plants and not damaging to your fish without a controller... and even turn off the CO2 at night... Provided you don't try to "draw down" the pH too much with the added CO2 when it *is* turned on.

I've got a Pinpoint pH electronic meter that doesn't have a probe. It's not a CO2 controller, just a pH meter. I'm pretty sure it still works. If you can get a probe, I'll mail you my meter to use for a few months. Then you can really see what's going on with pH/CO2 in real time. If you decide to get a controller, the probe you get will work on it too.

If you want to really push up the CO2 (and consequently really draw down the pH) then I would strongly recommend a controller.

Best of Luck...

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post #6 of 8 (permalink) Old 01-27-2003, 11:03 PM Thread Starter
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problem. I took a Ph reading this morning and it was 7.35 before the CO2 came on and at the end of the day the Ph came down to 6.8 (-.5).So I know what bubble rate i need anyway.All the plants are pearling by afdternoon .One thing I should mention is that all these fish when there sick or dying their body is half whitish like as if they were cooked.Its not a slime ,its a blanched white color under the skin.I wonder if I could have the timer kick on and off a few times during the nite to help keep the Ph more stabile.The pristellas are uneffected it seems as well as the otos and cory cat.

15gal planted,flourite+volcanite,65 watt pc,whisper 2 filter,5lb CO2 tank and diffuser,flourish .
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post #7 of 8 (permalink) Old 01-28-2003, 10:20 AM
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The closest match I can find for the way your fish look:

Obtained from

Milky cloudiness on skin -

Causes: Costia, Chilodonella, pH too extreme...


Symptoms: Milky cloudiness on skin.

This is a rare protozoan disease that causes a cloudiness of the skin. The best treatment is with copper at 0.2 mg per liter (0.2 ppm) to be repeated once in a few days if necessary. Acriflavine (trypaflavine) may be used instead at 0.2% solution (1 ml per liter). As acriflavine can possibly sterilize fish and copper can lead to poisoning, the water should be gradually changed after a cure has been effected.
Raising the water temperature to 80 - 83 F for a few days has also been effective.


Symptoms: Dulling of the colors due to excessive slime, fraying of the fins, weakness, gill damage

This disease causes a blue white cloudiness on the skin and attacks the gills. Later the skin may be broken down and the gills destroyed. The fish may behave like they have irritations, by glancing off aquarium decor, they may have clamped fins and difficulty breathing.
Acriflavine (trypaflavine) may be used at 1% solution (5 ml per liter). As acriflavine can sterilize fish, the water should be gradually changed after a cure has been effected. It also helps to raise the temperature to about 80 F.

pH too extreme

They don't post anything for this possible cause and in your case it sounds the most likely. However, I'd guess the solution is obvious... Stabilize the pH. Sounds like you've already done that!

Remember that an aquarium is just like the real world... There are all kinds of diseases lurking around that normally don't bother healthy fish. When fish are weakened, opportunistic infections of all kinds can pop up.

If you want to try to promote some healing, you might try adding a bit of aquarium salt. Just like warm saltwater helps a sore throat in humans, it can also promote healing in fish tissues. However, Cories don't like salt very much. 1 Tablespoon per 5 gallons is a recommended treatment. With the Cories in there, you might try 1 Tablespoon to 10 gallons. I have Cories too and I've used 1 tablespoon to 10 gallons in their tank in the past and they have tolerated it.

Slowly raising the temperature up to around 80 for a few days might also be helpful.

If you add the salt, do 20% water changes every day for a few days to slowly drop the salt concentration back down.

In fact, you might just want to read's "recommended treatment"... You can find it at:

Best of luck...

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post #8 of 8 (permalink) Old 01-28-2003, 10:07 PM Thread Starter
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This morning I came in and the CO2 flow was bubbling out like mad!!! AHha maybe thats the problem.I re set the flow and was happy to know I have a new needle valve on order .So maybe my old lab valve is just no good at holding flows.Ph was 6.3 when I checked it ,and it was only flowing for maybe 10-15 minutes.One has to really be on your toes when dealing with a 15 gal tank!

15gal planted,flourite+volcanite,65 watt pc,whisper 2 filter,5lb CO2 tank and diffuser,flourish .
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