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Interesting Tank Parameters
An intriguing case study to wet your appetites!
I was very surprised last evening when I visited a planted tank
enthusiast here in San Francisco and tested his tank water. I thought I
would share the information with you, and collect any thoughts you might
I'll describe the tank first. It is a 75 gallon Oceanic glass tank with
an overflow trickle filter and sump, about 18" wide, 21" tall and 48"
long. The substrate is 3-4 inches of plain silicon gravel without any
substrate amendments. Most of the gravel is fine 'plant sand' ~1 mm
with a top layer of coarser rounded gravel, somewhat larger than the 2-3
mm sand many of us use. The tank has been up and running for about 9
Lighting is a 4 - 55 W bulb compact fluorescent fixture from
CustomSeaLife. The bulbs are 6700K. The pressurized CO2 system uses a
Nupro fine metering valve and Eheim ceramic disk diffuser. Quite a bit
of CO2 was being pumped into the tank. I would guess CO2 levels were
~30 ppm which would put the pH in the 6.6 or so range. The sump return
was located near the surface-so there may be some outgassing of CO2 due
to surface turbulence.
Water changes are performed weekly with 40% -- 50% of the water being
changed out. Some carbonate buffer may be added at water changes (I
think it was SeaChem Alkaline Buffer, actually). As many of you know, we
are blessed with wonderful soft Sierra water here in San Francisco. GH
is about 3 deg. KH is about 3 deg. There are almost no macronutrients
in the water. K+ is about 0.5 ppm. Nitrates and phosphates are
negligible. Low levels of a variety of useful metals and minerals are
present. The aquarist adds Kent's Plant Supplement at water changes (I
do not recall the amounts).
The tank was sparkling clear with a full compliment of plants. There
was almost no visible algae on the plants and no algae on any of the
glass surfaces, which apparently do not require regular cleaning, even
for spot algae. Forgive my Latin spelling-I'm at work and don't have my
books at hand. A full stand of E. tenellus graced the front of the tank
as a 'lawn' plant. A large E. blerhi sword served as a center piece. A
variety of stem plants were growing well. These included H. polysperma
(rose variety), Ludwigia repens, water wisteria, Cardamine lyatra and a
corkscrew valisneria sp. Other plants included java fern, and a couple
of different crypts (probably wendtii and/or lutea and a small crypt
which I did not recognize).
The plants showed good growth, were generally large-sized, and showed no
signs of nutrient deficiencies. Three minor points may be worth
mentioning. An otherwise healthy stand of Java fern showed some signs
of blackish rot on a leaf or two. The small form of crypt had one or two
stems which appeared to be melting and a couple of older leaves on the
taller stand of crypt wendtii were beginning to be covered with a dark
grainy algae. These minor issues did not detract from the very
attractive and obvious healthy appearance of the tank.
Fish load. The tank is moderately to heavily stocked. There are 5
half-grown scalare/altum angels, a large school of fully grown
cardinals, several cichlids which were mostly hiding, a couple of bettas
and a few corys, if I remember correctly. The feeding regime is
apparently very heavy. Two large cones of live tubifex worms are kept
in the tank around the clock so that the angels can feed at any time.
Small colonies of worms are growing in the gravel.
Now for the shocker: Nitrates were over 50 ppm! (LaMotte Nitrate test
kit) and phosphates were over 1 ppm (Hach low range phosphate test kit)!
The aquarist said phosphates often measure 3 ppm with one of the
I asked about the history of the tank. There were significant algae
problems and the aquarist had changed out various species of stem plants
to find plants that were suitable for the conditions. He had resolved a
cyanobacteria outbreak with antibiotics. Over the nine month period
apparently the main strategy to achieve balanced conditions was to
reduce lighting intensity. The current light operation is to leave 2 of
the 55 W CF bulbs off all the time. The other two bulbs (110W total)
run about 12 hours per day. The aquarist has placed tissue paper
(Kleenex) under the fixture to reduce lighting intensity further.
Apparently, a stable, algae-free balance has been achieved in the
presence of high levels of nitrate and phosphate using light as the
limiting factor! The only other thought that came to mind was Diana
Walstead's iron-limiting approach to nutrient regulation. Although I
did not test for iron, none of the plants exhibited any signs of
So what do you think of these conditions (which I have never encountered
Steve Dixon in overcast San Francisco, with apologies for the long post