Report on peat substrate test

A 20gal (high) aquarium was set up as a 8 week test for a 
peat/dirt/vermiculite substrate to determine the reaction to the local water 
supply.  The ratio of substrate materials was 50:25:25, was 1 inch think 
with 2 inches of fine (2-3 mm) gravel on top.  Between these two layers was 
a single layer of 5-15 mm gravel, approximately one stone thickness deep. 
 At the end of the test, the 2" gravel layer settled to 1 1/2" deep.  Six 
days after the initial setup, the 7.2 pH had dropped below 6.0.  Alkaline 
buffer was added to raise the pH.  This trend continued for approximately 5 
weeks.  Weeks 6-8 found the pH dropped from 7.0-6.8 to 6.6-6.8 and no 
chemicals were added to the tap water.  The test kit used did not adequately 
differentiate between these two results.

         WEEK      0              1                2            3 
             4                    5           6            7            8
                  (tap water)
pH                     7.2       6.             6.2-6.4       6.0 
          6.0            6.2-6.4     6.6        6.6        6.8
nitrate                           12.5            6.0 
                            -                 12.5+
nitrite                                0                  0 
                            0                  0            0            0 
GH                     40        40                 -              - 
            40                  -
KH                     20           0                 -              - 
            45                  -
Phosphate     0.1        2.5                0             -               - 
                 3+           -             3

9gal water changes were made weekly.  Over the test period, additional 
plants and fish were added.  Initial fish were 1-4" Chinese Algae Eater, 
1-4" Beta.  Final fish were CAE, Beta, and 2 cory catfish.  Two Cardinal 
tetras were introduced during week 2 but did not survive.  I don't know if 
it was due to tank or fish conditions, or the fact that Beta was hungry.  I 
lean toward fish conditions because only 2 Cardinals out of 12 purchased 
over the last year have survived from this local fish store.  Cultured 
filter and separate sponge were placed in the tank to ensure adequate 
seeding of beneficial bacteria.

Initial plants were Amazon sword (echinodorus bleheri ?), red melon sword, 2 
ruffled amazon swords, 2 pygmy chain swords, hygrophelia polysperma and one 
potted micro sword.  During the last 3 weeks of the test, the fish barely 
had room to swim because there were so many plants.  Test results will be 
described only for the initial plants.  Green growth occurred in all plants 
until approximately week 4.  At this time much of the hygrophelia, both h. 
polysperma and "sunset" were at the top of the tank.  Frequent cuttings and 
rootings had expanded their number to fill approximately 1/3 of the entire 
tank.  After week 4, minimal growth occurred except in the hygrophelia. 
 Root growth for the Amazon sword, red melon sword and hygrophelia 
penetrated into the peat/dirt/vermiculite layer.  3-4 main roots penetrated 
deeply into the peat and 20-40 fine roots both in the gravel and the peat 
grew from the swords.  These had an approximate root ball  increase of 
50-75%.  The hygrophelia (bunch of 5 stems) had approx. 15-25 fine roots 
that penetrated the gravel layer and 5-10 that penetrated to the peat.  The 
2 ruffled amazon sword's roots increased approx. 25-40% with minimal 
penetration to the peat layer.  The pygmy chain swords lost their 2" long 
vertical leaves but developed 1" long horizontal leaves.  Approx 10-15 very 
fine roots penetrated into the gravel layer but one of the two plants grew a 
runner with 5-7 new plants on it.  The micro sword developed minimal roots 
and did not grow.

Penetration into the peat layer was determined 2 ways - (1) the amount of 
peat drawn to the surface during plant removal and (2) the color of the 
roots (peat roots were darker).  Fine roots tended to not disturb the gravel 
and peat as much as large root balls and many thicker main roots.  The 
peat/soil/vermiculite that was raised to the gravel surface was removed 
during a gravel cleaning.

The increase in Phosphate and continued amount of nitrate is a concern to 
me.  Possible factors include the tank being "light limited."  There was one 
15watt florescent grow bulb (14 hrs daily) and approx 3 hours of sunlight 
(one side of tank only).  Kent fertilizer was added weekly per instructions. 
 Minimal growth after week 4 was definitely due to light limitation.  During 
the first few weeks of a peat substrate tank, one must monitor the pH to 
ensure it stays within a reasonable range.   The KH must also be monitored 
due to the softness of the local water to prevent pH swings.

The permanent tank will utilize a similar substrate, with the ratio of 
peat/Georgia clay/vermiculite as 40:40:20.  An iron test kit was available 
the last week.  A separate test of peat, Georgia clay and food was conducted 
in individual test containers.  The Georgia clay was found to have Fe at 0.1 
where all other containers were 0.  The Tetra CO2 test kit did not react to 
test samples from any aquarium at any time, therefore CO2 levels are unknown 
for the test tank.
Rochelle Williams
williaro at ftmcphsn-emh1_army.mil
Mad Scientist in Training