[APD] CO2 levels and mega-dosing

["Karen Randall" <krandall at rdrcpa_biz>]

Tom wrote:

> CO2: always always always check this, 20-30ppm.
> 30ppm is better than 20ppm.
> DIY users beware.
> Always check at the end of the photocycle to see if you are low.
>
> Near as I can tell, I am the one that started the change in the CO2 levels
> from 10-15ppm to 20-30ppm.
> Prior, I had never once ever heard a single soul mention more than 15ppm
> for a plant tank anywhere.

Sorry Tom, you have been great at getting the word out in terms of "fighting
algae by growing plants" and you have done some great work actually pinning
down the values of nutrients that seem to be critical.  But I can't let you
take credit for this one. ;-)  Ines Scheurmann was advocating CO2 levels
between 20-30 mg/L as early as 1950 in Germany, and this information was
available to us in English here in the U.S. by the mid-80's. (hey, we were
30 years behind the times, but...)

The point where I heard 10-15 mg/L being popularized was when Tetra came out
with those horrible little diving bells and uncontrollable (and
unfill-up-able<g>) little CO2 systems.  My feeling is that they figured
they'd split the difference... 10-15 mg/L was better than none, and it gave
more margin for error before people started killing their fish.  I suspect
this second was a major concern with over stocked, under planted tanks with
too little light, and poorly controlled CO2 delivery systems.

> So why 20-30ppm?
> I based it on the plants response, fish? They where fine, I had Discus,
> Congo tetras etc.
> I also had much higher light than most folks.

Again, in the 80's, there was at least one article I remember in Aquarium
Today where an aquarist in Germany pushed the level (slowly and carefully)
up to 40 mg/L without harm to the fish in the tank.  This was done as an
experiment on the safety of CO2 use, however, I don't think you actually
need to keep levels that high.  The point was, there was a wide margin of
safety.  Personally, I've been keeping my CO2 level between 20-25 mg/L since
I started using pressurized CO2. (and before I met you ;-)

10 mg/L is just barely better than nothing.  You get 4 mg/L and can maintain
it steadily if you do nothing more than heavily aerate a tank.  And we know
that's not adequate under most circumstances.

> So if you add 2x more light, you'll need 2-3x more nutrients and CO2 is
> the first one to worry about.

Absolutely.  I know you know this, but I'll remind other people reading this
that plants are 43% carbon by dry weight.  This need MUST be met somewhere
if growth is going to be healthy.

> At higher light, you increase the frequency of dosing, NOT the volume.
> You can mega dose also about 12 hours before a water change with Macro's
if
> you want to "fatten" a tank up.
> You add 2x the macro dosing, then do a large water change afterwards and
> dose the normal amounts back.

OK, here's a question for you, Nutrient Meister.<g>  Do plants take up
nutrients at night or only during the photoperiod?  Are you better off doing
a "megadosing" like this in the morning, or just before the lights go out in
order to have the plants slurp them up as fast as possible?

Karen


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