Re: [APD] old soil substrate

["Jim Seidman" <js5 at seidman_net>]

josh bjork writes:
"I've got a soil substrate based tank that is a year or a year and a half
old.  It's 50gal and I used maybe a coffee can full of soil under poultry
grit.  It had a very nice growth spurt when the roots hit the soil.   The
growth has curbed significantly.  I have a medium fish load and give it
potassium occassionally."

"My smaller 20 gallon soil tank with 1 algae eater looks fabulous with no
care at all.  The tank has been running with no circulation for 6 months or
so.  What causes this fizz?  I would think the tank with fish would have
much more growth than one with an unfed algea eater."

With all due respects to Karen, I don't think the issue is inherent
unpredictability of soil substrates. Rather, my guess is that the 50g has
not nearly enough soil to support the plants.

One coffee can full is not much soil. In my tanks I generally use a 1 to
1.5 inch layer of soil on the bottom. This provides a huge store of
nutrients. 

Your 20g tank may have a thicker layer of soil, or simply less
nutrient-demanding plants. However, if you prune, you can be guaranteed
that the tank will eventually run out of nutrients as well, since you'll be
removing them from the tank without adding new ones.

Do you have a nitrate test kit? I have found that despite generous feeding
my macronutrient levels tend to plummet. Nitrate is a particular problem
because soil is a great medium for denitrifying bacteria. Regular dosing of
KNO3 and NaH2PO4 has made a huge difference. You might need to do the same.

Soil in sufficient quantities can provide enough traces to last for many
years. It can potentially provide enough macronutrients to last for a
while. Given the small quantity you used, I think you simply depleted it.

- Jim


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