Re: last ? before getting CO2

[Thomas Barr <tcbiii at earthlink_net>]

> From: Brown_D at pcfnotes1_wustl.edu
> Subject: Last question before investing in the CO2 system....
> 
> I've read in a couple of places that CO2 may not be required in a heavily
> stocked tank,

I disagree with this. Plant tanks need _less fish_ than what most would
consider "heavy". Adding more fish doesn't add more CO2 relative to the
plant's needs, it adds more NH4 waste which => algae. PO4 has little to do
with if you have good CO2 levels(this cannot be made up for by adding more
fish-CO2 gas needs to be added).
Try it for yourself and see. You'll find that the NH4 is the main cause of
algae. You can easily add NO3 in another tank without the NH4 and see this
difference. 

It also depends on what is acceptable for you concerning your tank. Some
folks don't mind more algae presence or poor plant growth.
Some folks want too many fish in a tank.

> since the fish and their waste are providing more input to
> the system; but on the other hand, most of the really spectacular
> algae-free planted tanks have relatively low fish-stocking levels, and CO2
> added.  

Many well run plant tanks can have higher levels of fish than a non CO2 tank
with less algae problems. Faster growing thriving plants will remove the NH4
faster when CO2 is being used. We can add NO3 from KNO3 instead of NH4 from
fish to help grow the plants and give them a good source of N. NH4 is not
something we would want to dose unless it's from fish load. At a certain
point the uptake rate and fish waste production will go over if you keep
adding more fish/critters to the tank. Plants can only absorb so much waste.
Of course you could get a bigger tank with more plants if you want to keep a
certain amount of fish/critters.

But the better you can grow the plants, the more fish you will be able to
keep in that tank of a given size. Everything has its limits but you can add
more if the plants take in more or uptake is faster. At lower fish loads
things are less likely to pass that point ever and the we supplement with
KNO3 for the plant's needs.
Adding some fish does provide NH4 which at very small amounts is good for
plants. Then you top off the needed N source for the plants with the much
less problematic NO3.
This is the safer more preferred method.

You can go with a non CO2 method but I would strongly caution not attempting
high fish loads to provide the CO2 and N. Lighter fish loads, lots of
herbivore and certain plants work well in those types of tanks.
Slower growth & less light etc = less uptake. You generally don't add KNO3
etc and everything goes into a nice deep substrate. Fish food and waste are
the main fertilizers here. It requires more patience, hands off, less plant
choices. 

Regards, 
Tom Barr

To put it simply, then, is the problem that if you put in enough
> fish to generate CO2 equivalent to adding it from a tank, that you also
> inevitably put in too many other nutrients too (particularly phosphates?),
> which increase algae growth at the expense of the plants?
> 
> Diane Brown