Water Chemistry

This is an important part of fish keeping and can be very confusing to both newcomer and experienced hobbyist. In this section I will try to keep the information relevant and to the point and I'll try to keep away from the things that we don't really need to know.

pH

Is measured on a scale from 0 to 14.  0 is the most acidic and 14 is the most alkaline, while 7 is neither one nor the other, it is neutral.

• Most freshwater fish live between pH 6.0 and pH 8.4, marine fish live between pH 8.1 to pH 8.4.

The pH in your tank can and does vary. It is important for the health of the fish that it does not stray out of the ideal parameters. In the aquarium there are lots of things that will change the pH. The following will cause the pH to fall (become more acidic);

• Fish, produce waste, this waste will ultimately become Nitrate. Some of this Nitrate (NO3 ) will form Nitric acid (HNO3) this means if you allow the Nitrates to build up in your tank through neglecting partial water changes the pH will also start to fall.
  
• Bogwood, contains lots of Humic acid, this will end up in the water and cause the pH to fall, This process will go on for years. Boiling the wood or soaking it for a couple of weeks before use will make little difference.
  
• Adding Carbon Dioxide (CO2) for the benefit of plants will also effect the pH. The CO2 will dissolve in the water, CO2 + H2O = H2CO3 which is Carbonic acid.
  
• Plants, although in theory will make a difference, In fact in the average tank they will have little or no effect. Only in the Dutch style planted aquarium where the plants are the main feature and the fish play a secondary role will their affect have to be taken in to account.
  
• Using peat in the filter or any where else in the aquarium.

There are also situations that can make the pH rise, this can also be damaging to some fish. A situation that is made worse because the water may also become harder at the same time.

• Shells, Coral, Tuffa rock, Limestone, Dolomite, will all affect the pH and raise it.

The pH scale itself is not very straight forward because it is logarithmic and each number on the scale is in fact not just a jump of one from the previous number but is a jump of x10.

• This means that pH 5 is ten times more acidic than pH 6, and pH 4 is one hundred times more acidic than pH 6 and so on.

For the fish this means that moving from one water to a different one must be done very gradually because what seems like a small change could actually be quite big, and send the fish into shock. 

Questions. and Answers on pH

1. How do I lower the pH?
   
   Answer: There are lots of buffers on sale that do the job for you very precisely, if you buy one of these make sure that it doesn't contain any Phosphates or Nitrates, as these will lead to an Algae problem.
   Also as mentioned above, filtering the water through peat will usually help. And it will reduce the KH Reading too.
   
2. How do I raise the pH?
   
   Answer: Crushed Oyster shells in the filter will help keep the pH well above 7. Usually to about pH 7.6. There are also various buffers for sale that allow you to choose the exact pH that you require. In an emergency Bicarbonate of Soda will raise the pH of a tank, should you discover the pH has fallen drastically.
   
3. Does the pH affect my fish in any other ways?
   
   Answer: Lots of ways, the effects of Ammonia poisoning are worse at high pH levels than lower ones. pH shock is every bit as bad as thermal shock, the filter bacteria work more efficiently at pH values above 7.5 and if the pH falls to below pH 4 (I think) Bacterial activity stops all together.
   
4. How often should I check the pH?
   
   Answer: If you keep sensitive species, especially in soft water, (Discus, Apistogramma's, Chocolate Gourami's etc) you should do daily checks, but generally a weekly check should be enough.

Water Hardness.

Put simply the hardness of water relates to the amount of dissolved Calcium and/or Magnesium salts in the sample. It is not the amount of dissolved solids in the sample, only Calcium and Magnesium count for measuring the hardness.

The units in common use to measure hardness are : - GH - general hardness, DH - degrees hardness, and KH - Carbonate hardness. DH and GH are equal to each other and 1 GH = 1 DH occasionally you will also see dGH this is also the same.

DH	mg/litre	Considered as
0 - 3	50	Soft
3 – 6	50 – 100	Moderately Soft
6 –12	100 – 200	Slightly Hard
12 – 18	200 – 300	Moderately hard
18 – 25	300 – 450	Hard
Over 25	Over 450	Very Hard

• Most fish live between GH 4 to GH 15, although they can usually be acclimatised to conditions outside their normal range.

GH/DH, or dGH, This unit refers to the Calcium and Magnesium Carbonates, Sulphate, Chlorides and is the total amount of these salts contained within the water.

Carbonate hardness or temporary hardness (KH) plays a more important role in the aquarium by keeping the pH stable. If the water has a high KH value and you want to lower the pH you can boil the water, this will break the chemical bond and the Calcium will stick to the heating element (it is this that furs up kettles in hard water areas) and Carbon Dioxide will go to atmosphere, leaving very little or no KH level in the boiled water.

The basic reaction is : - Water falls through the atmosphere and as it falls some Carbon Dioxide from the atmosphere is dissolved in it.

• H2O (Water) + CO2 (Carbon Dioxide) = H2CO3 (Carbonic acid). when this comes into contact with a stone containing Calcium (such as Limestone Ca CO3) a further reaction takes place CaCO3 + H2CO3 = Ca(HCO3)2 which is known has Calcium Bicarbonate or KH or temporary hardness.
  
• Temporary hardness is referred to as the buffering capacity of the water. For example if the water has very little KH hardness and you filtered it through peat which adds humic acid, the pH will fall very quickly,
  
• On the other hand if the KH is high the pH will remain stable until all the carbonates have reacted with the humic acid and then it will fall.
  
• So it is the KH level that prevents rapid changes of pH.
  
• For most fresh water fish an ideal KH level is between 4 to 8.

Questions and Answers about Water Hardness

1. How can I increase the General hardness of my water?
   
   Answer: In a number of ways, by using some Coral sand mixed in with the gravel, or by using Tuffa or Dolomite rock as a decoration, or by adding Magnesium Sulphate (epson salt) directly to the water.
   
2. How can I decrease the General Hardness?
   
   Answer: This is far more difficult, you need to dilute it with pure water from a de-ionisation or R/O (reverse osmosis) unit. Or by collecting rain water. There are some ion exchange resins that soften the water but they simply replace the Calcium and Magnesium with Sodium (Sodium doesn't count towards Hardness but the TDS (total dissolved solids) remains the same.
   
3. How Can I reduce the Temporary Hardness (KH)?
   
   Answer: Boiling removes all the KH rom the water, filtering through peat will lower it.
   
4. How can I increase the Temporary Hardness?
   
   Answer: By adding either Calcium Bicarbonate, Magnesium Bicarbonate or Sodium Bicarbonate.

Ammonia, Nitrite and Nitrate.

Ammonia NH3, This is a highly toxic substance that is produced by the breakdown of biological waste, it is also excreted by fish. Bacteria then oxidise this and it becomes

Nitrite NO2, This is also highly toxic to fish and causes the Haemoglobin in the fishes blood to become Methanoglobin, it is then no longer any use for carrying Oxygen to the fishes tissues which can result in ulcers or even death. Bacteria oxidise this even further and it becomes

Nitrate NO3. This is far less toxic and the levels are kept low by carrying out partial water changes usually in the order of 25 to 50 % per fortnight.