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Re: Soft water solutions
> Date: Thu, 10 Aug 2000 16:35:34 -0700
> From: "William Bragg" <williambragg at home_com>
> Relevant info:
> Tap water:
> ph: 7.1
> KH: 21 ppm
> GH: 13-16 ppm
With that pH and KH, The Chart indicates 2-3 mg/l CO2. This is a reasonable
amount of CO2 for water at equilibirium with the air. At least The Chart works
for your tap water - you only have carbonate buffers in the water.
> Aquarium (40gal acrylic:
> Actual amount of water closer to 30-35 gallons
Sounds good. Let's call it "125 liters".
> ph is 6.0 or lower in the tank
> OK my water is extremely soft. I assume the Jati wood is lowering my ph, but
> there is no discoloration of the water. The water is pretty clear, but I
> can not think of what else is lowering the ph at the moment.
With little buffering (~ 1 dKH), any acid will lower pH drastically. Aside from
any other things producing acidity, nitrification will add acid. The end
products of nitrification are H+ and NO3- (nitrate). This is the same as
titrating the water with nitric acid. The extra H+ by definition makes the pH
lower if it is not buffered. As H+ is added, it combines with the buffer to form
other compounds. Since the H+ is removed from solution by the buffer, little or
no pH change is seen. But the buffer is reduced by a bit. Once all the buffer is
used up, more H+ will lower the pH and the class "pH crash" occurs. Through this
mechanism, the pH can get down to 4.4 or so in an unbuffered tank with lots of
fish creating lots of stuff to nitrify.
> So to raise the KH I can add sodium bicarbonate (baking soda) or potassium
> bicarbonate, correct?
> To raise both the GH & KH, I add calcium carbonate, correct?
> So I can add baking soda or potassium bicarbonate and Seachem's Equilibrium,
How did Equilibirum get in here?
> But since the Equilibrium has potassium in it, I should use baking soda &
> Equilibrium, correct?
I think I would go back to baking soda or calcium carbonate. You can get calcium
carbonate from home brewing supply stores or chemical suppliers like Hach
Chemical (www.hach.com). Anything is probably cheaper than fish store products.
> Or I can use sea shells or coral, correct?
You can but they are harder to control.
> Then I can add CO2.
> Are any of these solutions more prudent,
When you add baking soda or calcium carbonate, you know what you are adding.
It's hard to say the same about other methods. Yes, shells, coral, marble and
limestone are mostly calcium carbonate but who knows what else is in there as
> Speaking of the initial amount, the fish I would like to keep
> appreciate the soft water, so what is the relationship of CO2, pH and KH
> I should be shooting for? Am I missing the boat entirely?
You didn't miss the boat but it's rocking dangerously. :-)
When you say the fish like soft water, that means GH (General Hardness) which is
the amount of calcium and magnesium. GH is the kind of hardness that has
biological affects - cell development, egg development, strong bones, etc. Fish
and plants that are adapted to a certain level of calcium and magnesium in the
water will do poorly at very different levels (but may adapt over time). So,
figure out what GH your fish need and adjust accordingly.
Note that "figure out what GH your fish need" is not as simple as it sounds. For
example, just because wild discus live in very soft, acidic water doesn't mean
that the discus you have came from very soft, acidic water. If you are buying
wild fish, adjust your water for their natural habitat. If you are buying
captive bred fish, adjust your water for what they were bred in (might be hard
to figure out).
Likewise, your fish may want a specific pH range for the same reason. Find out
what they need. Then, balance KH and CO2 to get that pH.
KH/pH/CO2 is NOT related to "biological hardness" (or softness).
And, just to complete the dissertation, watch out for other hardness terms. We
are concerned with KH (Carbonate Hardness) which is the amount of carbonates or
bicarbonates in the water. KH affects pH. KH is usually determined with an
alkalinity test with the assumption that carbonates are the only buffer in the
water (this, alkalinity = KH). If other buffers, such as phosphates, are in the
water, alkalinity does NOT equal KH and your "KH" test kit may be off.
We are also concerned with GH (General Hardness) which measures calcium and
magnesium present in the water.
Ignore terms such as total hardness, temporary hardness, permanent hardness,
etc. They may be equivalent to what we need to know but they are confusing and
are only meaningful to other endeavors such as running boilers. GH and KH,
that's all you need to know.
> I assume I would add the necessary ingredients at every water change (not
> referring to using shells, etc.). But how much at each water change, if I
> change 1/4 to 1/3 every other week? Not the same as the initial amount,
Correct. Let's do an example. First:
One teaspoon (about 6 grams) of sodium bicarbonate (NaHCO3) per 50
liters of water will increase KH by 4 degrees and will not increase
general hardness. Two teaspoons (about 4 grams) of calcium carbonate
(CaCO3) per 50 liters of water will increase both KH and GH by 4
degrees. Different proportions of each can be used to get the correct
KH/GH balance dictated by the fish and plants in the tank. Since it
is difficult to accurately measure small quantities of dry chemicals
at home, a test kit should be used to verify the actual KH and GH that
Now, let's start with 125 liters of water at 1 dKH, 1dGH. Let's say you want to
keep the GH as it is (soft water fish) and want to have a 7.0 pH. For good plant
growth you want 15 mg/l CO2. Checking The Chart tells us you need 5 dKH. So,
what must we do to add 4 dKH to 125 liters?
Simple - add 2.5 teaspoons of baking soda. Then check with your KH test kit to
see how close you came - it's hard to measure small quantities of dry chemicals.
After you add that, your pH will increase. In theory, with 2-3 mg/l of CO2 and 5
dKH, your pH will rise to 7.7 or so. Now add CO2 to bring the pH to 7.0 and you
have the right amount of CO2.
Of course, you may want to add part of the baking soda, add some CO2 to bring
the pH back to 7, add some more baking soda, etc to avoid pH shock. Especially
if your water is currently at 6 or so.
Let's do a more complicated example. Let's aim for a GH of 3 (increasing it by
2) and a KH of 5.
If we add 2 1/2 teaspoons of calcium carbonate, it raises the GH & KH by 2. Then
adding 1 1/4 teaspoons of baking soda raises just the KH by 2 more. The use your
GH and KH test kits to see what really happended and season to taste.
When you do water changes, add enough baking soda and/or calcium carbonate to
bring the amount of water you are adding up to the right level. If you change
1/4 of the water, divide the amounts above by 4. It might be useful to adjust
the amount of water you change to produce even teaspoon measures of stuff.
> I am sorry for all the questions. I have spent hours searching the
> archives, sometimes going down dead end threads, etc. I am doing my best to
> provide a healthy environment for the plants and fish as I feel is my
> responsibility. Any help is appreciated.
Hope this helps.
George Booth in Ft. Collins, Colorado (booth at frii_com)