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Laterite quantity, substrate circulation & reptile under-tank he

> From: "E. Keith Johnson" <zekj2 at Access_ETSU-Tn.Edu>
> Date: Wed, 26 Jun 1996 16:35:25 +0000
> 
> Regarding the use of laterite, how does one calculate a quantity to
> use?

If you are using Dupla laterite, use 500 grams (a little over a pound)
for 50 gallons.  

If you are using modeling clay, fashion a 1/8 size replica of
Michelangelo's "David" from a 25# bag then use what is left over.  Or,
if the clay has a higher iron content, do a 1:100 model of the Empire
State building and use what is left over.  Unless you plan to grow
crypts.  In that case, also use the top 3 stories of the building.
No, seriously, I don't know.

> I'm considering the same substrate set-up approach as Granger Ridout,
> that is, a base of vermiculite, laterite & fine gravel mixture and
> fine gravel on top...awaiting comments to his post.

Why use laterite?  If you are using vermiculite, I would think you
would want to use top soil or loam instead.  IMHO, you don't need to
use vermiculite when you have laterite.  
 
>  I have one additional idea I would like to solicit comments on.
> Since circulation is important in the substrate, I was thinking of
> taking half-inch CPVC with numerous holes drilled in it and running it
> throughout the substrate to facilitate circulation.  I was going to
> place it on top of the vermiculite with a clear tube coming up from
> the network in the back of the tank to add nutrients and fertilizers.
> A couple of air stones could be placed inside to aid the movement of
> water when CO2 is turned off.

If you have circulation, you want it to be BELOW the substrate
additives so that nutrients are transported to the CEC sites.  Also,
it sounds like you will be pulling water into the PVC.  I suspect the
holes will get plugged very quicky and this will be ineffective. 
It would be much better to treat this as a reverse-flow UGF and
somehow push water OUT of the holes.   

Also, a 1/2" PVC manifold will be very bulky.  How big is the tank?
 
> A couple of air stones could be placed inside to aid the movement of
> water when CO2 is turned off.

It is not wise to turn the CO2 on and off since you will have much
larger pH swings than if you left it on all the time.  And it is
especially not wise to aerate when the CO2 is off if you insist on
turning it off since the aeration will allow CO2 to diffuse out of the
water faster, causing a quicker pH rise.

> To further treat the substrate, I was thinking of using the "Heat
> Wave" reptile undertank heaters by Hagen.  There are three sizes up to
> 25 watts and they are reasonably priced.  

> Any comments?
 
$ SARCASM ON $

Well, this will certainly be a showcase of substrate techniques. 

$ SARCASM OFF $

I like to use 1.5 to 2 watts per gallon of water for substrate heat,
distributed evenly across the substrate. Of course, I use heating
coils to generate convection currents and you already have the PVC so
all you need is something to warm the gravel.  Perhaps a more cost
effective technique would be to use a string of the larger Christmas
Tree bulbs arranged around the bottom of the tank.  Surely it would be
less costly than reptile heaters.

George