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Scheel Letters: Fry and the low values of pH
Courtesy of
ARK - Arizona Rivulin Keepers
The Scheel Letters, No. 12
Fry and the low values of pH
In one big tank with about 300 fry of Cynolebias (Cynopoecilus) melanotaenia, a few fry
of Nothobranchius and some fry of Cynolebias whitei after some days had a few hydra
possibly coming up from the bottom. This was treated with sulfuric acid in the way
that the pH that was about 6.0 was decreased to about 4.0 (endpoint of brome cresol green)
within one hour. All fry were apparently unaffected and so were daphnia and cyclops
but all hydra next morning were white and died. In another tank I saw some green
hydra and decreased the pH possibly far below 4.0 (water showed pure yellow color
a few hours after using brome creol green, then I found lots of "white" fry dead on
the fine peat mud but also I saw many fry swimming all over the tank. I added little
tap water and no more fry died. Now there are many "calliurum" but no "labarrei" in
this tank. Adding acid to the water of this tank indeed was made "by eye" and no doubt
the pH was decreased far below 3.8. Another tank with breeding pairs of Epiplatys
bifasciatus was infected by green and "red" hydra by large numbers. Fishes were
transferred to another tank. The pH of the water was decreased to about 4.0.
All hydra disappeared. None was seen during the following 3 weeks. Yesterday
I lifted out 40 sound fry. The fry of this species always hide themselves and
you only are able to estimate the number of fry from the consumption of food, just
the way you do when breeding characins. Fry measuring 15-20 mm have distinct crossbars
on the sides of their bodies and quite a number.
The Balanced Aquarium
Aeration using pure carbon dioxide
We all know that plants need a steady supply of certain elements if they shall
live and grow bigger and bigger. These elements are primarily carbon (C), hydrogen (H),
oxygen (O), nitrogen (N), sulfur (S), phosphorous (P), potassium (K), calcium (Ca),
magnesium (Mg) and iron (Fe). Secondary other elements may be of importance: boron (B),
manganese (Mn), copper (Cu), zinc (Zn), molybdaen (Mo) and possibly also gallium (Ga).
The secondary "nutrition elements" very often are very poisonous if present in
concentration up to 1 ppm (mg/l).
In the balanced aquarium which possibly is of great importance when keeping
the more feeble species of killies we want the plants to continue to consume all
waste products which the fishes give away. Not only the carbon dioxide should be
removed from the water by the activities of the plants, but also the nitrous components,
possibly this being much more important.
If aquarists did not crowd fishes in their tanks, if they at least would
give sufficient light, if they did not overfeed, possibly they would have a better
aquarium keeping. The development of the inexpensive aquarium pump (diaphragm type)
certainly has not made things easier to the fishes in the tanks. Certainly by this
way he may get rid of the surplus carbon dioxide formed by the surplus of fishes in
his tank, also he may to a certain degree increase the supply of oxygen to the tank.
But he cannot blow out the nitrous waste products from the fishes.
Through the years I have acted (more or less involuntarily) as a sort of
"fish doctor" to the aquarists of this country and from this service I conclude
that most troubles in the aquarium keeping at level of the common aquarist comes
from tanks far out of balance because of a much too high number of fish, insufficient
lighting and cleaning of the bottom layer. I always wondered why people want so
many fishes in their tanks. They never seem to have enough. Changing this bad
habit is very difficult. People who more or less "live on the hobby" are in two
ways interested in this matter because they think that they will sell more fishes
primarily and secondarily more fish will die, but they do not take into consideration
that they force many people out of this interesting hobby.
As a breeder by passion I certainly have faced these problems many times.
As the fry grow up the previously so well established tank more and more comes out
of balance. My best helpers -the "water ferns" (Ceratopteris)- loose their handsome
live green color, they turn into a light green color, and at the same time the "algae
pest", the blue green algae (Oscillatoria, etc.) appear. This is a warning, in
particular to the man who keeps the feeble species of killies. Well you say, give
more light and certainly sometimes this may help, but after some time the problem
arises once more. Renewing the water only helps for a very short time. You have
to lift out the fish, discard the water ferns, wash the sand or peat and reset the
tank. Well, this is not a severe problem as long as you only deal with smaller
tanks, but tanks that hold more than 100 liters (25 gallons) you do not want to
reset every two months.
A month ago I had to reset my biggest tank - 320 liter that like all other
tanks in my fishroom has a bottom layer of old peat and peat moss. This tank was
far out of balance, caused by overfeeding, insufficient light during wintertime and
so on. Also there was a lot of hydra all over the tank. Fishes were caught, plants
removed and the whole dirty bottom layer of peat was stirred up. In order to kill
the hydra, phosphorous acid and sulfuric acid was added until the reaction was pure
yellow using bromo cresole green as indicator (pH bellow 4.0). Water now was very
turbid indeed. Next day lots of daphnia were introduced. As usual they were not hurt
by the low pH value. The daphnia gradually cleaned the water. Several times the
bottom peat was stirred in order to help the daphnia in their cleaning work. The pH
increased rapidly after each adding of acid caused by the buffer action of the peat,
so more acid -much more indeed- had to be added in order to keep down the pH value
between 4.0 and 5.0. As this tank is made of stainless steel and has the bottom
sheet of stainless steel uncovered, this adding of acid to the peat could be dangerous.
No doubt lots of metallic ions were liberated by the "regeneration process". As
copper chloride had been used several times in this tank against hydra and Oodinium,
the very poisonous Cu-ions absorbed by the peat may be liberated by the acid or
certain heavy metallic ions from the stainless steel absorbed over years by the
peat may go out into the water. This did not happen as the daphnia were not killed.
After some days, the water and the peat seemed to be sufficiently clean and
Cryptocorynes, Aponogetons and big water ferns were introduced. In order to
increase the supply of carbon dioxide, I filled one liter bottle with 1/3 concentrated
hydrochloric acid and 2/3 water. A rubber plug with a piece of glass tube, connected
the carbon dioxide developer to the "aeration stone" of the tank (I never use "stones"
because most material here used possibly will dissolve in the water, therefore I use a
little piece of plastic hose with little pressed perlon inside for the formation of
small bubbles). Pieces of marble and chalk were put into the "CO2 developer" and
soon lots of fine bubbles of pure carbon dioxide were rising from the "aeration stone".
Light was turned on during all nights and very soon a heavy growth of the ferns was
easily seen. This proved that the water still held lots of nourishment for plants.
Snails were introduced to clean the leaves of the Cryptocorynes and soon the tank was
once more apparently balanced.
Since the "carbon dioxide developer" actually was at hand, why not use it in
other tanks? A 260 liter, 2 meter tank had big males of Pterolebias peruensis, several
smaller species of Aphyosemion and some Procatopus. The tank had been out of balance
during the spring months but was now in apparently good order. Now I began to blow
this tank with pure carbon dioxide in order to see how the fishes would behave. After
a few hours (light on night and day) plants began to give away oxygen as fine bubbles
and the growth of the water ferns increased. Possibly this tank, that was very overcrowded,
had a need of more carbon dioxide in order to remove a surplus of plant food. The
aquarist who for some time has used a demineralization filter or has used oxalic acid
in order to prepare soft water, knows that a certain amount of carbon dioxide will
kill his fish within a few minutes. Many fishes possibly have been killed when they
were introduced into tanks with unaerated demineralized or dechalked water. Within a
few minutes the fishes are paralysed, they seem to be dead, and if they are not at
once put into normal water they surely will be dead in a short time. I know that
outflow from my demineralization filter treating water with 5 degrees of alcality (SBV)
will kill my fishes in that way. 5 degrees of alcality correspond to 5 milliequivalents
of acid used to neutralize the temporary hardness (and/or "soda hardness") in one liter
of water. 5 degrees of alcality correspond to 5.22 = 110 ppm (or mg/l) of CO2
liberated by the acid (or in the filter), but the tap water contains even more
carbon dioxide. In order to keep a temporary hardness, corresponding to 5 degrees
of alcality (that is 5 ml of 0.1 normal HCl in 100 ml of water) in true solution, a
rather large excess of carbon dioxide is needed. To a temporary hardness of 5.2 = 14
German degrees corresponds about 34 ppm of CO2 and also that tap water normally holds
about 20 ppm of free CO2. That will say that this water, after treatment that removed
the temporary hardness, contains about 165 ppm of free carbon dioxide.
The well known books on fish diseases written by Schueperclaus and Reichenbach-Klinke
do not give exact information on the values of free carbon dioxide that fishes will tolerate
in very soft water. In his book "Diseases of Fish" van Duijn wrote about some experiments
with a goldfish in water containing up to 300 ppm of carbon dioxide, but the pH during this
experiment is not known and may play a role. Not long ago I read some paper which gave some
values, but I do not remember where I read it, I only remember the value 50 ppm of carbon
dioxide as critical.
Carbon dioxide resolves in water to a high degree. Water in contact with pure
carbon dioxide will resolve about 1650 ppm at room temperature and normal barometric
reading. (0 C = 3350 ppm, 10 C = 1688 ppm, 30 C = 1260 ppm). Normal air only contains
about 0.035% of CO2 by volume, that is about 1/3 cubic centimeter in each liter of air,
that will say that normal air in contact with pure water will force this to take up
about 0.5 ppm at 20 C. Freshy collected rain water normally contains 0.5-2 ppm of CO2.
Stagnant water in nature may have 2 ppm or more near the surface but the deeper water
normally contains much more. In polluted rivers up to 50 ppm were found, but in normal
rivers only 0-2 ppm of CO2. Some years ago I measured the concentration of CO2 free in
my rain forest tanks. Rarely I found values up to 20 ppm.
The very high solubility of carbon dioxide in water makes the aeration, using
pure carbon dioxide, rather dangerous when fishes are present in the tank. On the other
hand this sort of aeration may be of value and, if used with care, I think it may be
used without great risk. Estimate the critical value of about 20 ppm CO2 in rain forest
tanks with very soft and low conductivity water.
CaCO3 + 2 HCl = CaCl2 + H2O + CO2
(40 + 60) 2(1 + 35,5) 40 + 71 44
100 73 100 44
100 grams of chalk or marble treated with 73 grams of HCl will form 111 grams
of calcium chloride and 44 grams of free carbon dioxide. Common hydrochloric acid
holds about 470 grams of HCl in each liter of acid. As I dilute 1/3 part of acid
(by volume) with 2/3 parts of water, my solution holds about 157 grams of HCl in
each liter. My bottle holds 1 liter of diluted acid. In order to use all acid
this solution I have to add about 215 grams of water-free chalk or marble to the
water and this will give me about 95 grams of carbon dioxide (about 50 liters of
carbon dioxide). The calcium chloride formed will easily resolve in the water,
as this salt resolves by 745 grams in each liter and here only about 240 grams
are formed. Approximately 2 grams of chalk or marble produce 1 gram of free carbon
dioxide. If in 100 liters of water I will not press more than 20 ppm of CO2 that
is 20.100 = 2000 mg or 2 grams. Put only 4 grams of marble in the bottle and keep
light on until the plants do not give away any more bubbles of pure oxygen.
I will keep you informed on further experiments and experiences drawn from
my future using of this method. Possibly the common method of aeration using common
air does blow out much too much carbon dioxide from the water and the plants are not
able to take up the other waste products formed by the fishes.
Aeration using Pure Oxygen
Not very often (I hope) you feel a need of blowing your aquarium water with
pure oxygen, but breeders now and then must face the situation where polluted water
forces the fishes to the surface and where lots of oxygen is needed to clear up the
situation. A good "pure oxygen developer" is easily constructed. Hydrogen peroxide
(H2O2) in contact with manganese (MnO2) freely will liberate pure oxygen and this
development may go on for more than 24 hours. Use a simple glass bottle. Place some
pieces of manganese (MnO2) in this bottle and fill it up with water. Add little
liquid hydrogen peroxide and soon you will see minute bubbles rise from the manganese.
When you are transporting fishes on journey such "oxygen developers" may be a great
help. Do not try to plug the bottle if oxygen comes out, the bottle will explode.
