Oxygen level?

[Watcher74]

I bought a book to learn about setting up and maintaining a heavily planted aquarium.

It talked about the oxygen level dropping throughout the night until the fish start getting stressed and to only agitate the surface water at night to promote gas exchange (-CO2 +O2), but not to do it during the day to keep the CO2 for the plants.

I plan on using a CO2 injector and getting a timer to turn on the lights/CO2 and off at the same time. But what about surface disturbance?

I'll have a timer for CO2 and lights but have to manually adjust the filter outtakes?

How can this be done more conveniently? A timed bubbler or something?

 

[Leopardess]

You might not even need to worry about any of that.

You only might need to think about that if you notice your fish gasping for air in the morning, or if you cannot keep your co2 below 25ppm.

It sounds like you're getting a pressurized system...so you could easily adjust how much co2 you're introducing.

I've found, and mostly what I've seen agrees, that it is generally best to avoid stopping the co2 at night. It can lead to pH fluctuations. Running an air stone will force the co2 out of the water, and the pH will go up. In the morning, the decreased air introduction, combined with increased co2 introduction, will put more co2 in the water and can cause the pH to go back down again.

The only reason behind what you read about are that plants stop taking in co2 at night - so the levels can rise. I haven't found this to ever be a problem, however. Granted, I don't use pressurized, but even the night of refreshing the co2 system, I dont have any problems.

 

[djlen]

Test for the kH of your tank, No. 1.
Don't inject without knowing it.
When you find that it's 3.0°H or above you can then safely set up your CO2 system.
If you have a tank of 20 - 30 gals. or larger there is little risk of over-dosing DIY CO2 using a 2-liter bottle.
If you plan on a pressurized system, you should start it up early, on a day that you can monitor your pH/kH relationship every hour or two and adjust it to no more than 15-20ppm while the lights are still on. This will give you a cushion of 10 - 15ppm of safety for the fish. Test again for content the next morning at lights on and see what you have. If it has risen to, say, 25ppm over night, leave it alone an see how it reacts that day and the following night before adjusting again. A good needle valve will stay at the same adjustment indefinitely so the pH should not waver.
A timer for lights is always a good idea. Turning off CO2 or bubbling off CO2, IMO, is wasteful and unnecessary.
The only thing I would be concerned about regarding returns from filters is, 'are they gassing off and wasting my CO2'.
Go here:
http://www.csd.net/~cgadd/aqua/articles.htm
On this site you will find, among other great articles, an article on Setting up a planted tank. And calculators for measuring CO2 levels and nutrient dosing.

Len

 

[anonapersona]

Well said! djlen

Hit that nail squarely on the head!

Once the system is up and running smoothly, it is useful to test to see if turning it off makes any real difference. When the system is off at night, you might see no real difference in morning and evening pH values and then you just save gas and delay the refilling process. I haven't seen any difference. But I don't run the daytime levels very high, either.

OTOH, you might see a swing in pH that is too much, I think you just have to test it in your own tank with your consumption levels from plants, your o2 consumption from fish in the day and both fish and plants at night, your input level, your outgassing level, your buffering level, and adjustments for fish and plant growth. Just too many varibles to know (9 variable equations, anyone?)

 

[Watcher74]

Wow. Ok, I'm glad I'm studying this months before I'll be doing it. I've got a lot to learn.

Thanks to everyone. You've given me a lot of good info I'll be keeping in my notes.

 

[superjohnny]

Shutting off CO2 at night is what a solenoid is for. You plug it into a power strip and run it off a timer. I inject CO2 and don't bother shutting it off at night and my fish are happy & healthy.

 

[plantbrain]

I've always shut the CO2 off at night and cranked it in during the day.

I hear people suggest that pH variation from turin gthe CO off at night is somehow bad or harmful for fish, this is simply and plainly not the least bit true. This is very easy myth to dispel.

Water changes often involve water that is a full unit or so different than tank water. If the pH changes rather than the KH/GH changes were really the cause...............we'd all have dead fish for anyone that does weekly 50% water changes..........

I'd done 50-70% water changes each week for decades, with Discus, Altums, Apistos, Cardinals, Otto cats etc, they love the water changes.

Now if pH changes causes stress on fish and is somehow bad, why have I never had a single disease in 20 years?

Why does Amano turn off the CO2 on all his tanks?
Does his fish look stressed?

CO2 induced pH changes are quite different than adding KH buffers or things that drop the pH like H3PO4.

We add CO2 for the plants, not for pH control although you can determine the CO2 by the pH measurement.

Diurnal pH variations in lakes and ponds that have heavy vegetation can go from 6 to 10 in 12 hours, more typical ranges are 7-10, tidepools in SW go from 8-10 in 4-6 hours.

This occurs naturally every day. Rain events also change the chemistry.

Fish are fine.

Over dosing the CO2 will poison them, but they do not gain anything from a stable pH vs the off gassing at night of CO2.

Remember at night you have a lot of O2 built up during the day and generally the tank is over 100% and it's giving off O2 most the 24 hr peroid.
About 2 to 8 hours per day it might fall below 100% in a well run tank.

Add some(not alot) surface turbulance, you can always add a little bit more CO2 easy enough that is wasted from that.
You can also use a surface skimmer and not need any surface turbulance at all.


Regards,
Tom Barr

 

[daveedka]

Tom,
I've been following this as well, and am a bit confused by your last post. Do you reccomend or feel it's necessary to turn off the co2 at night or are you simply dispelling the myth that it is harmful to do so.
Dave