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Re: Biowheels-CO2-plants redux

At 11:52 AM 9/15/99 -0500, Dan Dixon wrote:

>I knew I was losing some CO2 via the biowheels, but just didn't know if the
>loss outweighed the overall benefits. Since I was getting acceptable CO2
>readings with them on (probably since I slowed my wheels down) I didn't want
>to ditch them without justification. You'll note I say "was," because I'm
>currently experimenting with them off for comparison of water chemistry with
>them on. So far, I have more CO2 (duh), possibly even too much; getting
>around 25mg/L in the AM with a .7/sec bubble rate. Since I can't really slow
>my yeast generator without risk of spraying the walls with a Zima-like
>substance <g>, maybe the biowheels could serve as a regulator for the CO2

That's one of the reasons I _do_ use them in small tanks.  I'd rather run
slightly low on CO2 than kill the fish!  On big tanks, it's hard to
generate enough CO2 with yeast to cause a problem, and if you are
purchasing bottled gas, you usually have a more reliable delivery system.
It also makes little sense to buy gas and then purposely get rid of it!

>Oh yeah, forgot to mention that. I have about 50 community fish (most an
>inch long or so) in this 45 gal. Is this high or low?

That's a little on the high side.  The way to tell for sure is to see if
nitrate and phosphate reading creep up between water changes.  If so, You
probably need the extra filtration.  OTOH, a better solution would be to
lower the fish load!<g> (biological filtration does nothing to solve
phosphate problems, and this is the larger issue from an algae standpoint)

>Is the consumption of nitrate by the bacteria really significant? 

No.  The aerobic bacteria used in the "nitrogen cycle" do _not_ consume
nitrate.  They simply convert it from something more poisonous to something
less poisonous.  The problem is that ammonium is a _better_ food source for
the plants than nitrate, which requires the expenditure of more energy for
the plants to process. (though that's probably not _terribly_ significant)
The point is, why feed it to the bacteria at all, if you have the right
ration of plants/animals that the PLANTS can use the ammonium being
produced within the system.  

Also remember that nitrifying bacteria cling to EVERY surface in your tank.
 This includes the glass, all equipment, the gravel, and the plants.  There
is a _tremendous_ amount of surface area in a planted tank.  Unless the
tank is WAY over stocked, there is more than enough surface area to provide
homes for all the bacteria you need, without also using biowheels or other
bacterial filter beds.

>They seem to have left enough for the algae.  

This is a sign of too many fish/too much feeding for the plant mass.
Bacteria simply convert ammonium (a plant food source) to nitrate (a less
dangerous to the fish plant food source)  If you've got algae problems, the
plants can't use all the "food" you're giving them.  The bacteria convert
it to nitrate, where it is _still_ available in the water column for algae
to use. (and again, this also means that phosphate levels are building,
since the bacteria don't touch that.

>BTW, can anyone recomment a good,
>sensitive, accurate nitrate test kit?


IMO, we spend much too much time worrying about the absolute accuracy of
test kits.  It doesn't _matter_ what the absolute values in your tank are.
It matters that you can track _changes_ and correlate those to the health
of your plants and signs of visible algae.  A nitrate level acceptable in
one person's tank may be WAY too much in another tank with different
lighting, feeding, etc.

You need a _low range_ phosphate kit.  I currently am using and am
satisfied with the Aquarium Systems "SeaTesT" kit.

I have the low range SeaTesT nitrate kit, but find that it is TOO low range
for most applications.  It tops out at 1ppm using the low range method, and
10ppm with the mid-range method.  The Tetra nitrate kit is cheap and
reliable.  It starts at 12.5ppm, but a level of about 1/2 that can be
easily detected by eye.  If you are struggling with an algae problem, you
probably could use both range tests, particularly in an over stocked tank,
where it is likely that your nitrate level is high enough that it will only
read as "really red"<g> with the SeaTest low range kit.  If you need to
track ADDITIONS of nitrate in a nitrogen poor tank, the Tetra kit is
probably enough to do the job.

I'm not saying these kits are the only ones that work, or even that they
are "the best".  They are the ones I happen to have on hand, and have
learned to handle reliably for MY PURPOSES.  I have used other test kits in
the past.  There are a few that I would not purchase again.  There are
others that the only reason I changed was because these tests were on the
shelf when I needed a new one.  I have not used them personally, but I've
heard enough reports of inconsistent results here on the APD that I would
_not_ purchase Red Sea test kits.  OTOH, I am yet to be convinced that it
would benefit me in any way to spring for the expensive Hach or LaMotte
test kits, even though I am willing to believe that they are more
"accurate" in the absolute sense.


>Couldn't fast growth rate in a densely planted tank cause CO2 levels to
>temporarily fall below equilibrium by "sucking" up all the CO2? 

Yes, if you are not supplementing with a sufficient amount of CO2.  It's a
bad situation though, as the plants then begin to spit carbon from the
water, lowering the KH.  It also slows their growth, which can give algae
the advantage in a high-light situation.  If you _can't_ provide enough CO2
to keep the level above equilibrium, (or at least not below)  it is far
better to lower the light level, and stick to plants that are low light,
slow growth species.

I wrote:

>> They become more of a problem when CO2 rate drops, unless it drops to the
>> point that CO2 in the tank is LOWER than at equilibrium with the
>> atmosphere.  Then, again, the biowheels could help alleviate that
>> situation. 

You wrote:

>Most of the
>time my CO2 levels are above equilibrium (usually over 10), but on occasion
>they will drop to below 5. (Like when the CO2 generator is about spent--less
>than 1 bubble every 3 secs.) Or are you referring to other possible causes?

Sorry, I was referring to a drop in CO2 production from your yeast reactor,
not a drop in the CO2 levels in the aquarium.