CO2 & Surface Agitation Debate-Please Comment!
Dave Millman
Several planted aquaria club members got into a debate about CO2 and
surface agitation a couple of nights ago. Below is the consensus we came
to. I think we got our facts straight in the end, but there are a couple
of extreme cases we wanted to confirm.
In all cases, assume a planted tank with both fish and a cannister
filter.
NO CO2 INJECTION:
Surface agitation is GOOD: without it, plants will extract the CO2,
driving pH up, particularly in tall tanks. CO2 levels in non-injected
tanks don't go above about 3ppm regardless, so surface agitation keeps
the level at or near that point. Fish don't exhale enough CO2 for the
plants, so it is much more productive to encourage CO2 diffusion in from
the atmosphere than to try to retain the fish output.
TANKS WITH CO2 INJECTION:
Surface agitation is BAD, as it allows precious CO2 to outgas. However,
fish need O2, so a balance must be struck. Plants produce O2, but only
during the light period, and they consume some during the dark period.
Larger fish will typically be the first to start gulping air at the
surface when not enough O2 is present. Unfortunately, pl*cos and some
other fish can suffer badly from inadequate O2, so experiment carefully.
OPTIONS FOR INJECTED TANKS:
Maintain enough surface agitation such that fish never gasp at surface.
Pay close attention to fish in the morning before lights come on, as
this is the point of lowest O2 concentration in the water.
Consider adding an air pump and air stone which comes on when the lights
go off. This will increase circulation when it is needed most, and when
CO2 is needed least.
If you have PRESSURIZED CO2, a little more surface agitation is not
quite as critical as with DIY, as bottled CO2 is relatively inexpensive.
My own experience was that increasing agitation meant I needed to
increase my bubble rate only incrementally to maintain the same pH,
raising annual CO2 costs from about $12 to about $15. The increased
agitation allowed sufficient O2 that the fish never did their gasping
act.
INJECTED TANKS WITH TIGHT COVERS
In this case, outgassing CO2 can accumulate under the cover, displacing
atmospheric O2, which will dramatically lower O2 levels in the water.
The only solutions here are to loosen the cover, or to add another O2
source, typically an air pump and air stone.
VARIABLE CIRCULATION RATES OF CANNISTER FILTERS:
As the filter material clogs, cannister filter circulation rates tend to
go down, decreasing circulation and surface agitation. You may have
enough agitation to keep O2 levels high right after you clean the
filter, then be severely O2 deficient as the filter clogs, especially if
your bio load is high or your filter is small for the tank.
WHEW! Did I get it all? Thanks in advance for any corrections/updates.
Chuck Gadd
<davemil...@spamyahoo.com> wrote:
>Surface agitation is GOOD: without it, plants will extract the CO2,
>driving pH up, particularly in tall tanks. CO2 levels in non-injected
yes.
>Maintain enough surface agitation such that fish never gasp at surface.
>Pay close attention to fish in the morning before lights come on, as
Just maintain good water circulation. This will increase the amount
of water in contact with the surface air, which increases the O2
level.
>If you have PRESSURIZED CO2, a little more surface agitation is not
>quite as critical as with DIY, as bottled CO2 is relatively inexpensive.
I agree.
>INJECTED TANKS WITH TIGHT COVERS
>In this case, outgassing CO2 can accumulate under the cover, displacing
>atmospheric O2, which will dramatically lower O2 levels in the water.
Your list looks very complete.
Chuck Gadd
http://www.csd.net/~cgadd/aqua
Christopher
it run for a 125g tank yearly?
"Chuck Gadd" <cg...@cfxc.com> wrote in message
news:0vo54vgge7q2jf8t2...@4ax.com...
Jim Miller
would be 10lb tank would last most of a year if not more. fill at beverage
distributors, fire extinguisher service outlets, welding suppliers. look for
them in the yellow pages.
10lb refill is probably $20 or less on average.
jtm
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"Christopher" <UC...@ucla.edu> wrote in message
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Richmond
> it run for a 125g tank yearly?
http://www.dlink.org/aqua/CO2.html
Hope this helps
Dominic
Dave Millman
>
> Your list looks very complete.
>
Chuck,
Thanks for checking it for us!
tcb...@earthlink.net
Well growing plants will send the dissolved O2 levels well above 100%.
Less surface agitation is needed when you grow the plants well.
Although I tried using air stones at night etc, I've never found a
need.
It really is as simple as grow the plants well.... and everything else
will fall into place.
I seek some slight movement on the surface, a surface skimmer is very
nice and no current is needed at the surface with one of these. But
good mid and low level currents in the tank are very condusive to
plant growth in all cases.
Regards,
Tom Barr
m walczak
planted tank with DIY CO2 injection. Initially, when I step up the
tank I was just getting into fish again and did not plan on a planted
tank. Heres my problem:
I can not get my pH below 7.5. I have a UG filter and it agitates the
surface along with my over the back filter. I have gone to the
extremes of adding another bottle. one has an actual fine bubbler
stone and the other has a fairly large bell diffuser. I dose with PMDD
and my other stats are as follows,pH 7.5 KH 6, GH 9,NH2/3 0, NO2 0,
NO3 .15, Fe .10, Phos 0, 3.8 wgp (i defiantly need co2). Any
suggestions on how to lower my pH? MY plants are growing well but I
have a small fuzz or hair algae problem and growing red/ bread algae
problem, that has been ongoing for a couple months now and I think it
may be do to low co2 since there is little or no pearling most of the
time. And I think this low co2 may be from too much surface ag. Any
suggestions on possible solns?
of lower co2 or more importantly the algae...
Dave Millman
> Well growing plants will send the dissolved O2 levels well above 100%.
> Less surface agitation is needed when you grow the plants well.
>
> Although I tried using air stones at night etc, I've never found a
> need.
> It really is as simple as grow the plants well.... and everything else
> will fall into place.
>
> I seek some slight movement on the surface, a surface skimmer is very
> nice and no current is needed at the surface with one of these. But
> good mid and low level currents in the tank are very condusive to
> plant growth in all cases.
Tom,
Thanks for the comments!
redled
Just a comment about my setup. I use a powerhead to diffuse DIY CO2 in my
tank. When I first started using it, I had it at the top of the tank, and it
always locked because of gas buildup. I moved it to the bottom of the tank,
in a cave, and put it upside down. Now it no longer gets locked, it's
quieter, diffuses more CO2 (the cave acts as a bell) and as an added bonus I
get "free" water circulation at the bottom layer. Just thought I'd throw that
in there, in case someone else has a similar setup. You might as well maximse
the use of your equipment if it can do two jobs at once.
__
"Insert witty comment here."
-John
Dave Millman
One issue at a time:
You say you cannot get your pH below 7.5, despite 2 simultaneous bottles
of DIY CO2. Please clarify: What is the pH of your aquarium water WITHOUT
CO2 injection? In most cases, two bottles of DIY CO2 should be more than
adequate to drop pH in a 29 gallon tank by 0.5 to 0.8.
Secondly, your tank stats look good, except for phosphate. Plants need
more than zero phosphate! An archive search turns up discussions like
these:
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&th=ce4ce2bdbf87a635&rnum=1
m walczak
PO4- and it checks in at about 10 ppm. Acceptable. I agree that i
should see an increase with two bottles. I added the second one to see
if could get a further drop. Not much. I want to get my co2 in the
area of 15ppm, ideally. One thing that comes to my mind is that the
bubbles being released from the UG filter heads are contributing to
excess CO2 surface exchange and limiting the formation of pH lowering
carbonic acid. What would be the consquences of terminating the use
of the UG filter? Is it feasible to do this?
I am correct in saying that allowing the CO2 to enter into my over
the back of the tank filter that the bacteria would be put in a
comprimising situtation due to the exposure to the forming carbonic
acid? Hence this would not be a suggested manner to diffuse the CO2.
Thanks.
Dave Millman
> My pH before CO2 injection over 3 months ago was ~7.8 I rechecked my
> PO4- and it checks in at about 10 ppm. Acceptable.
I'm not a phosphate expert, but this sounds very high. you should do more
research, perhaps by searching the archives on Google Groups on
"phosphate"
http://groups.google.com/groups?as_q=phosphate&as_ugroup=rec.aquaria.freshwater.plants
> I agree that i
> should see an increase with two bottles. I added the second one to see
> if could get a further drop. Not much. I want to get my co2 in the
> area of 15ppm, ideally. One thing that comes to my mind is that the
> bubbles being released from the UG filter heads are contributing to
> excess CO2 surface exchange and limiting the formation of pH lowering
> carbonic acid.
If the CO2 bubbles do not dissolve in the water, they do you no good.
> What would be the consquences of terminating the use
> of the UG filter? Is it feasible to do this?
If you turn it off, the bacterial action in the gravel will go from
aerobic to anarobic (sorry for the spelling). This could cause problems
for your fish.
> If there
> I am correct in saying that allowing the CO2 to enter into my over
> the back of the tank filter that the bacteria would be put in a
> comprimising situtation due to the exposure to the forming carbonic
> acid? Hence this would not be a suggested manner to diffuse the CO2.
> Thanks.
Over-the-back filters arenlt the best at dissolving CO2. The tend to do an
incomplete job, and lots of CO2 can escape right out the top or in the
spill-over.
Regarding the bacterial reacting adversely to the carbonic acid, that is
not reported to be a problem.
Read up on CO2 reactors, and see if you can't get more of the CO2 you
already have to dissolve.