Re: Laterite Question

[Ken Simolo <Simolo@chem.chem.rochester.edu>]

>
>Well, Matt, yes and no. I really can't speculate what caused your
>changes, but I would bet the laterite is the culprit. I'll give you 4
>different ones I studied: (pH measured with equal amounts of DI
>water and laterite, Orion meter)
>
>Substrate Gold - pH = 4.9, soft, will disintergrate when disturbed,
>causing all kinds of mess. 4-5% Fe.
>
>First Layer Pure Laterite - pH = 5.7, medium hard to soft, will cloud
>water when disturbed. 11-13% Fe.
>
>Dupralit G - pH = 6.3, soft, will disintergrate. 8-10% Fe.
>
>And now the kicker: CaribeSea Laterite - pH = 9.8 ( yes, that's
>right!) hard as a brick, will not cloud water once rinsed, no rxn
>when treated with HCl, so no CaCO3/MgCO3 to drive the pH up.
>Actually had the same amount of Ca as the previous three. 0.4-1%
>Fe.

I would just qualify your findings by mentioning that your DI water 
has almost no buffering capacity.  Therefore, the pH measurements 
will indicate a potential problem but not necessarily a real problem. 
To find out if the laterite is a really problem under "normal" tank 
conditions, you would need to titrate it with a known concentration 
of acid to see how much alkalinity it has.  Now, if you have no 
buffering capacity in your tank because you are using almost pure DI 
water, then you do have a problem.

Ken


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