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Aging substrates

Joe Hildreth wrote:

>On the subject of long term substrate slowing down after 12-18 months, I
>have notice the same thing in most of my tanks.  After many years of
>keeping plants in a soil based substrate, i know that if I replace the
>old substrate with new soil, the tank will be very robust for another
>year.  Currently, I am working with substrates that are 2 or more years
>old trying to keep things growing in an acceptable manner.
>I would appreciate hearing opinions on what has changed in older
>substrates and how we plant keepers can maintain an older substrate.

I have kept lots of tanks going, and with excellent growth for many years
without replacing substrates.  The current "oldest" is about 5 years old,
but I've had them going longer, it's just that I've recently (within the
last year) traded in several smaller tanks for two larger tanks.  

I have one newer tank set up with Seachem Flourite, and so far, I'm pleased
with the tank.  Time will tell how it ages.  But my "standard" tanks have
all been set up exactly the same way.  3" or more of approximately 1mm
gravel with laterite mixed into the bottom 1/3-1/2 of the substrate.  In my
older tanks I used Dupla laterite, and for the last several years have used
Substrate Gold with equal success and less cost.  I use little or no
substrate fertilization after initial set up. In the "old days" I used
Dupla fertilizers.  For that past several years (about 5, I think) I've
used exclusively TMG for trace element fertilization, supplemented with
KNO3 as needed.  My tap wat supplies a small amount of PO4 with water changes.

In my tanks, slowing of growth even when appropriate levels of light, CO2
and other nutrients are maintained has _always_ been a sign of too much
plant mass in the tank, and often that includes a heavily root-bound
substrate.  This is usually at about the 18 month mark, but can happen
earlier in a very high growth tank.  When it happens, I feel around in the
substrate with my fingers.  If I can't easily get into the substratea in
most areas of the tank, it's time for a major plant pull.  

This isn't "trimming", this is pulling up all plants in one area of the
tank by the roots, and thoughly gravel vacuuming that area of the tank.
Yes, you pull out some laterite, but lots is still left behind.  I usually
find that I can replant about 1/3 of the plant mass that I take out, and
the tank usually looks "full" as soon as I'm done... It's amazing how
quickly plants crowd a container when they are growing well.  One exception
is that I usually leave stands of Crypts in place and untouched unless they
are spreading into areas I don't want them in.  They seem to do better left
alone.  It makes a mess, but it's worth it.  You won't be able to see
through the tank when you get done, but at least using the brands of
laterite I work with, the tank will be back to normal clarity in the next
day or two.  The plants take off growing vigorously immediately, and the
tank looks much better than before it was "attacked".

Claus Christensen is the person who first suggested this to me, and his
advice was to do 1/3 of the tank every couple of months so as not to
disturb it TOO much at once.    Since I started doing this, I have gone to
doing 1/2 the tank with one water change, and the other half with another
water change about 2 weeks later.  I have had no problems with this at all,
either in terms of algae problems or stress to either plants or fish.  I
have even, on occassion, stripped out an entire tank and reset the plants
in one setting without having a problem, though this probably isn't the
best way to start.  I have never yet taken a tank apart specifically to
replace a substrate in all the years I've been keeping planted tanks... I'm
too lazy.  I find a way to keep them working.

One other word of caution... If you have any nocturnal catfish like striped
raphaels, make sure any dense stands of plants go into a bucket, and not
out on a table unattended for long periods... and DON'T start dividing
large plants with a knife until the fish are accounted for.  My 10 year old
raphael has ended up in the kitchen sink twice during these division
sessions... thankfully we do _not_ have a garbage disposal!<g>