Water Hardness and pH

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Water Hardness and pH

• What it means for a tropical aquarium

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What is Water hardness?

• Basically, it is the amount of dissolved minerals
  present in the water.
• Water hardness is of interest to aquarists for
  two reasons
• to provide the proper environment for the fish.
  
• to help stabilize the pH in the aquarium.
• There are two types of water hardness general
  hardness (GH) and carbonate hardness (KH).

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General Hardness (GH)

• General hardness is primarily the measure of
  calcium (Ca) and magnesium (Mg) ions in the
  water.
• GH is commonly expressed in parts per million
  (ppm) of calcium carbonate (CaCO3), degrees
  hardness (dH) or, more properly, the molar
  concentration of CaCO3.
• One German degree hardness (dH) is 10 mg of
  calcium oxide (CaO) per liter.
• In the U.S., hardness is usually measured in ppm
  of CaCO3. A German dH is 17.8 ppm CaCO3.

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General Hardness Parameters

• 0 - 4 dH, 0 - 70 ppm very soft
• 4 - 8 dH, 70 - 140 ppm soft
• 8 - 12 dH, 140 - 210 ppm medium hard
• 12 - 18 dH, 210 - 320 ppm fairly hard
• 18 - 30 dH, 320 - 530 ppm hard
• higher liquid rock (Lake Malawi and Los
  Angeles, CA)

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What does this all mean for an aquarium?

• When a fish or plant is said to prefer "hard" or
  "soft" water, this is referring to GH. Incorrect
  GH will affect the transfer of nutrients and
  waste products through cell membranes and can
  affect egg fertility, proper functioning of
  internal organs such as kidneys and growth.
  Within reason, most fish and plants can
  successfully adapt to local GH conditions,
  although breeding may be impaired.

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Carbonate Hardness (KH)

• is the measure of bicarbonate (HCO3-) and
  carbonate (CO3--) ions in the water.
• In freshwater aquariums of neutral pH,
  bicarbonate ions predominate and in saltwater
  aquariums, carbonate ions begin to play a role.
• Alkalinity is the measure of the total acid
  binding capacity (all the anions which can bind
  with free H) but is comprised mostly of
  carbonate hardness in freshwater systems.
• Thus, in practical freshwater usage, the terms
  carbonate hardness, acid binding, acid buffering
  capacity and alkalinity are used interchangeably.
• In an aquarium, KH acts as a chemical buffering
  agent, helping to stabilize pH. KH is generally
  referred to in degrees hardness and is expressed
  in CaCO3 equivalents just like GH.

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Buffering

• If you add a strong acid such as nitric acid to
  water, it completely dissociates into hydrogen
  ions (H) and its "conjugate base" or "salt",
  NO3- or nitrate.
• The hydrogen ions freed in the reaction then
  increase the concentration of hydrogen ions and
  reduce the pH.
• Since nitric acid is the end product of the
  nitrogen cycle, this explains why aquarium pH
  tends to decrease and nitrates tend to increase
  over time.
• When the aquarium has some carbonate buffering in
  it, the bicarbonate ions will combine with the
  excess hydrogen ions to form carbonic acid
  (H2CO3) which then slowly breaks down into CO2
  and water.
• Since the excess hydrogen ions are used in the
  reaction, the pH does not change very much.
• Over time, as the carbonate ions are used up, the
  buffering capacity will drop and larger pH
  changes will be noted.
• From this it is clear why aquariums with low KH
  seem unstable - as acid is produced by biological
  action, the KH is used up when it is gone, the
  pH is free to drop rapidly as H ions are
  generated.

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ADJUSTING FRESHWATER HARDNESS DOWNWARD

• If your local water is too hard for the fish and
  plants you desire, it can be softened.
• There are many ways to do this but some are more
  suited to aquarium use than others.
• The best (and most expensive, of course) is to
  use a reverse osmosis (RO) deionizer and mix the
  resulting water (GH0) with tap water to get the
  desired GH.
• Peat moss can be used to soften and condition the
  water for use in South American cichlid tanks,
  but will add a slight tea color to the water.
  Peat filtering may be difficult to control. Peat
  should be boiled first to kill any unwanted
  organisms.

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ADJUSTING FRESHWATER HARDNESS UPWARD

• If the local GH is too low, it can be raised by
  adding calcium sulfate and/or magnesium sulfate.
  This has the drawback of introducing sulfates
  (SO4--) into the water, so care should be
  exercised.
• Calcium carbonate can be used, but it will also
  raise the KH (this is ideal for the lucky few who
  have naturally soft water). Various combinations
  can be used to produce the desired results.

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ADJUSTING CARBONATE HARDNESS

• Carbonate hardness can be reduced by boiling the
  water (inpractical for all but the smallest
  aquariums let it cool before adding to the tank
  -) or by peat filtering.
• Carbonate hardness can be easily increased by
  adding sodium bicarbonate. Calcium carbonate will
  increase both KH and GH in equal parts. 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 is achieved.

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What is pH?

• pH is a measure of the acidity or alkalinity of a
  substance.
• pH is measured on a scale of 1-14 with 7 being
  neutral. Something with a pH lower than 7 is
  acidic. Something with a pH higher than 7 is
  basic.
• Water has a pH of 7 naturally, but the water you
  are using in your tank will be different because
  of the chemicals that are suspended or dissolved
  in the water.
• These chemicals fall into three categories
  acids, bases, and buffers.
• Acids are chemicals that lower the pH, or make
  the water more acidic.
• Bases are chemicals that raise the pH of the
  water, or make it more basic (or alkaline).
• Buffers are chemicals that can 'tie up' acids or
  bases and keep the water at a specific pH.
  Different buffers will keep the pH at different
  values.

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What Can I Do to Change the pH Slowly and Safely?

• If you want to lower your pH safely, add a piece
  of wood to the tank as a decoration or add some
  peat to the filter system, but be aware that this
  will stain the water yellow or brown for a couple
  of years.
• If you want to increase pH, add a sea shell or a
  coral skeleton. Remember, these will not give you
  immediate, overnight results, but they will
  introduce buffering agents to the water to help
  keep the pH more like you want it.

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What is the water like out of the tap?

• How can we start with something different?
• Answer Mimic Nature

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What makes water soft in nature?

• Rainwater is slightly acidic (6.8) and VERY SOFT
  (0-4) since it has no dissolved minerals. Hence,
  it has no way of buffering, so it is extremely
  susceptible to pH swings.

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What makes water hard in nature?

• Dissolved minerals from igneous rocks will raise
  the general hardness.
• Dissolved limestone will raise the carbonate
  hardness.

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What makes water acidic?

• Tannic acid from organic material (i.e., leaves)
  lower the pH.

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The Goal

• To recreate your fishs environment as closely as
  possible