CO2 and O2, Fertilizers

Subject: CO2 and O2 in the planted tank

From: (Karen A Randall)
> > 
> > OK, when you wrote this in the last post, I thought you might 
> > misspoken, but here you are repeating yourself.  While plants 
> > respire, they do _not_ add to the CO2 levels in the tank (unle
> > are rotting) They use _much more CO2 than they give off.  Like
> > while they do use some O2, they give off _much_ greater amount
> > photosynthesis.
Subject: CO2 and O2 in the planted tank

George Booth said:
> Minor correction - plants use CO2 and give off O2 only during
> photosynthesis.  When they are not photosynthesizing, either whe
> lights are off or because conditions are not suitable, they prod
> CO2 and use O2 just like everything else.

That's what I thought I said.<g>  I guess I should have said that 
_over a 24 hour period_ (assuming good growth conditions) plants 
will GIVE OFF more O2 than they use, and will USE more CO2 than 
they give off. 

Subject: Fertilizer

>In light of the recent re-post of PMDD's I have been wondering if 
>the people that use these actually still use Slow rlease 
>fertilisers that are added weekly or with every water change? Can 
>I get by by purely using Duplarit (or whatever they call the gold 
>dust) and PMDD's??? 

The fertilizer that works best for me with my water chemistry is 
Tropica Mastergrow.  Unfortunately, it is not sold in this 
country, so I have a hard time getting a hold of it.  

I have used it dosed with water changes as directed.  There has 
always been measurable amounts of iron at the next water change, I 
have never had any adverse effects, and it does more for my plants 
than anything else I've used.

When I can't get Mastergrow, I use Duplaplant 24 (daily) and 
Duplaplant tablets, (with water changes) for almost as good 

What about the recent post on the analysis of fertilisers, has 
this been done scientifically or is it just speculation. George, 
if Dupla Drops are purely Iron why on earth are they so expensive? 
Is Dupla saying that plants only require Mg, Mn and Fe. Shorly 
their fertiliser regieme consists of more chemicals than these.

I think, from speaking with Kaspar Horst, that the reasoning 
behind their specific mix of minerals, (and he stresses that both 
should be used together) is that the others are _usually_ found in 
tap water in adequate amounts.  Obviously, there will be a great 
deal of variation between one tap water supply and another.  

I suspect that the reason my plants do a little better with 
Mastergrow than they do with Dupla, is that there is either 
something that is not supplied in sufficient amounts by my tap 
water, _or_ that the excess amounts of copper in my tap water 
interfere with the uptake of some other mineral.

>I have been using an Australian made Aquarium fertiliser for some 
>time now that seems to provide enough of everything but iron. I 
>dont use daily drops. Im going to make some PMDD's but wonder if 
>I should continue using the current fertiliser. I will have to 
>look at the ingredients. Only tests will tell what to do I 

Knowing that they are that close in composition to Mastergrow, I 
may very well try them too, (when I find the materials and the 
time ;-) although I will _not_ include nitrate in the basic mix.  
I understand Kevins reasons for using it, but I would want to be 
able to fine-tune the application of nitrate separately from my 
trace element mix. Particularly when I know Mastergrow seems to 
produce the best growth in my tanks, and it does _not_ contain 

> Surely no one fertiliser is superior to the other. 

Some are _definitely_ superior to others!  Some still contain 
substances that encourage algae growth, some are not properly 
balanced, some contain substances that are of no value to aquarium 
plants (although you are still charged for them) and others are 
just not a good value in terms of trace elements/$$.

>On any given day plants will grow at a different rate and 
>therefore require a differnet amount of elements than the 
>previous day. With that said fertilisers should be aimed at 
>providing an average amount of each element required for 
>excellent daily growth. Therefore, wouldnt PMDD's be the best 
>fertiliser on the market (provided that the average of chemicals 
>is taken from a large test???) Any comments? Im not a chemist 
>(far from it, I have problems just identifying what all the 
>letters mean), 

Again, I think what is best for your plants depends on what you 
have in your tap water.  Some people will do better with a slight 
different mix than others unless everyone is starting with RO 

>am I missing a vital point, ie some chemicals reacting into an 
>undesirable state?

There _are_ some minerals that will not stay in a useable state in 
the water column, and these minerals are usually supplied either 
via the reducing environment of the substrate, and/or are chelated 
to remain available for the plants to use for a longer period.  
Other minerals are dangerous to both plants and fish in more than 
minute amounts.

Karen Randall
Aquatic Gardeners Assoc.
Boston, MA