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My small change on soil substrates

Jacques wrote:

>I've been following the "discussion" on the merits or lack thereof of 
>the various substrates. Here is my personal experiance.
>I'm currently running a soil substrate 50L (about 10 gallon) tank. 
>I've got yeast CO2, 3.6 watts per gallon of 6500K Osram Biolux 
>daylight tubes with polished aluminium reflectors, no filtration, 
>20% water changes every three weeks.
>Anyway the substrate is 1cm of local red subsoil, then about3 cm 
>of clay topsoil mixed 1/2 and 1/2 with vermiculite, then a layer of 
>swimming pool filter sand, also about 3 cm. The tank has been running 
>for about four months now. I'm getting growth that even my colleagues 
>can't believe (I'm a botanist).
>Tank has seventeen species of plant. My Mexican Oakleaf is growning 
>right out of the tank, my three species of Ludwigia and my Hygrophila 
>would if I didn't prune them every three weeks, my Limnophilia has 
>taken over the back of the tank, 

I have to say that if you get by with pruning a 10G tank with that much
light and all those fast growing species every 3 weeks, you are getting
_far_ less than the growth that could be expected in the wild.  And far
less than could be expected in an optimally balanced aquarium either.  Of
course, you may be purposely retarding growth, but from your post, that
doesn't seem to be your goal.

I'm glad you're enjoying your tank, and I'm glad that you are happy with
the growth you are getting.  But I don't think that the growth rates you
are reporting do anything to advance the theory that soils substrates
produce "better" plant growth in the aquarium.

>and I scoop off about 1/2 square 
>foot of some Lemnaceae species (its not Lemna, rather a related 
>genus) every week. I fertilise with MgSO4 and K2SO4 according to 
>Steve's recipe, although I haven't added fertiliser for a month and a 
>half now. I stopped adding the KNO3 as it seemed to be causing algea 
>problems. The only algea I can see in my tank is some on the side of 
>the glass in the soil layer, and a fair bit of thread algea that I 
>just remove mechanically. Anyway it doesn't bother me.

Again, I'm glad that the algae doesn't bother you, but it's not a
resounding endorsement of the method either.

>Things like laterite just aren't accessable here (they're available 
>here, just very expensive. A typical fishtank light cost costs what 
>I earn in two days.)

It certainly is true that dirt from the back yard is cheaper... if you
don't count the worth of your time to process it.

>All I can say is that soil substrates work. You need to set up a 
>soil tank properly before you can judge whether soil tanks are good 
>or not. Sure not all soils are  equal. The local soil I used is 
>rather poor. If anything that's why I chose it in the first place, to 
>ensure that the substrate wasn't too fertile. The vermiculite was 
>originally just me combining Steve and Jim's recipe's, but now I use 
>it because of its CEC. I have a suspicion that after the initial 
>algae bloom, it captures much of the dissolved nutrient ions and 
>keeps it from entering the watercolumn. The Chem department agrees 
>with me on this.

As George has mentioned, and I've said numerous times on this list, there
is _no_ reason that people should feel that it is necessary to endure an
"initial algae bloom" .  I've set up dozens of tanks, all showing growth at
least as good as what you describe, (many better)  with "low fertility, low
CEC" laterite/gravel substrates.  _NONE_ of them have experienced algae
problems even in the initial phase.  The shortest term of these tanks has
been @ 9 months, (school tanks taken down at the end of the school year)
the longest term tank is now 7+ years old.

The _only_ tank that I have had ongoing stability problems with of one sort
or another for 2 1/2 years now, is a soil based tank.

I know that there are people who like soil substrates, have found a good
local soil supply to work with, and have learned to manage soil substrates.
 But it is just one of a number of methods that can work very, very well if
handled properly.  It is my belief that laterite/gravel substrates are much
easier to manage, particularly for the novice.  I know for a _fact_ that
one can achieve _excellent_ growth in a laterite/gravel tank.

>Sure my substrate isn't natural. I wouldn't use pond mud if you paid 
>me too, especially here in SA. All those Noo-Noo's are a bad idea in 
>what is essentially an artificial environment.  

And that was where I believe Olga started this conversation.<g>

Karen Randall
Aquatic Gardeners Association