As water passes from our tap, into our koi pond where it circulates for several weeks and is then discharged during a partial water change, it will experience different chemical processes. Having covered the basics of pond chemistry in the previous article, let’s take a look at some of the chemical interactions water may experience on its journey through a koi pond.
1. Water Purifiers
The vast majority of us depend on tap water as the source of the pond water in which we keep our koi.
It is standard practice for water companies to add certain additives to water to make it safe or better for human consumption (chlorine, fluoride) where as our koi demand water with as few additives as possible. Our water companies have a legal responsibility to provide us with water that is safe to drink. They do not however have the same duty of care for our fish’s requirements, and it is our responsibility to take what is suitable for humans, and with a purifier, make it more suitable for our koi.
Time for a little more chemistry.
Water and the solutes dissolved within it are made up of ions. Ions are atoms that are electrically charged and are commonly the building blocks for other molecules. Their charge may be positive or negative, depending on the type of ion, with every ion having a charge which cannot change. In electrolysis, which involves the use of two oppositely charged electrodes (negative and positive) to separate out ions in a solution, the positive electrode is called the anode and the negative electrode is called the cathode. Consequently, negatively charged ions are attracted to the positively charged anode (and are therefore called anions), where as the positively charged cations are attracted to the negative cathode.
For example, if salt (sodium chloride) is put into water, it dissolves and then dissociates into two separate ions – a positive sodium ion (or cation, Na+), and a negatively charged chloride ion (or anion, Cl-). So in solution, sodium chloride no longer exists and it’s ions are free to move and combine with other ions of an equal and opposite charge.
Consequently, all ions can be split into two groups; the positively charged cations such as calcium, magnesium, sodium, iron (all metals) and the negatively charged anions such as bicarbonate, carbonate, chloride, sulphate, nitrate etc.
Fortunately, the vast majority of impurities and inconsistencies between our tap water and that of pure water are due to an excess of specific ions. And as these ions will either have a negative or positive charge, with a little applied chemistry, we can target and remove these offending ions using a water purifier before they enter the pond.
______________
BOXOUT: What is the difference between absorption and adsorption?
A sponge absorbs water into the inside of it’s porous structure. Ion exchange resins are not porous and so we describe the action by which they attract and retain ions on to their surface as adsorption.
__________________
What is ion exchange?
Ion exchange is a reversible chemical process in which the specific ion (such as sodium, Na+) are released from the insoluble solid medium (which is the ion exchange resin) and exchanged for none-desirable or target cations such as heavy metals. There are two types of ion exchange that can be caused to occur within a water purifier; that which removes target cations and that which removes target anions.
How cation exchange works.
Cation exchange resins are usually made from an inert compound called polystyrene-divinylbenzene which is heated in its manufacturing process with concentrated sulphuric acid, causing a sulphonic group (SO3-) to be permanently fixed on to the structural chemistry of the resin beads. Because these sulphonic groups have a negative charge, they can be charged with positively charged ions (cations) typically sodium (Na+), potassium (K+) or even hydrogen (H+). When tap water containing dissolved cations (such as heavy metals) pass by the resin, then these are exchanged for, and trade places with the loosely held sodium ions on the resin. There will come a time when no more cations can be removed by a fully reacted resin which is then described as being ‘exhausted’, and which must then be replaced. The better a resin is protected by pre-filtration from fouling contaminants such as iron and chlorine (which can actually cause the resin polymer beads to disintegrate), the longer it’s active life will be. Cation exchange resins will remove most metallic, positively charged ions such as barium, cadmium, copper, iron, manganese, zinc, calcium and magnesium.
This leaves the negatively charged contaminants or anions which must then be removed before the water can be used to fill a koi pond.
How anion exchange works.
Anion exchange units use a different resin that works in the opposite way to a cation exchange resin. It is charged with either chloride (Cl-) or hydroxyl (OH-) ions, which will then be released into the pond water in exchange for the less desirable contaminant anions. Anion exchange removes nitrates, sulphates and other negatively charged ions.
2. Zeolite
Zeolite is an off-white clay-like mineral that has desirable chemical adsorbing properties. It’s use in the koi world is as an ammonia adsorbing substrate that should be used as a short-term remedy for peaks in ammonia brought about by overstocking, overfeeding or filtration problems. As a means of chemical filtration zeolite should be placed as late in the filtration process as possible. Its porous nature makes it very liable to clogging, and it’s efficiency declines greatly if it is allowed to do so.
Zeolite works by itself being slightly negatively charged, bonding loosely to sodium ions which attach to its surface. In the presence of the ammonium ion (NH4+), ammonium ions become adsorbed to the zeolite in exchange for the sodium ions which are released into the water.
Zeolite has a limited effective lifespan, where its ammonia adsorbing properties decline over time. At such a time, it should be removed to be ‘recharged’, rejuvenating its useful properties so it can be used again. Zeolite can be recharged by placing it in a bath of salt water for 24 hours. The ammonia is released into the water and the Zeolite is ‘recharged’ with the sodium ions; ready for use once again.
Ideally, there should not be a call for Zeolite to be used in a koi pond that is managed wisely. It is only required during an ammonium crisis, which if one occurs, can soon be remedied by stopping feeding and carrying out a partial water change, saving on considerable expense.
3. Clays
It is widely recognised that koi exhibit their best health, colour and vitality when they are kept and reared in a clay pond (often referred to as a mud ponds). In fact mud ponds are a Niigata koi breeders’ key resource for producing the world’s finest koi. These ponds are cut out of clay-rich earth, forming a naturally watertight and mineral-rich base on which to grow koi. The water is highly turbid as koi forage in the muddy substrate, stirring up the ultra-fine clay particles, keeping them in suspension.
We keep koi in highly filtered clear water ponds for our benefit, so that we can see them in all their resplendent glory. But by doing so, we are making a compromise between what we want and what is best for our koi. One way of improving the quality of life for our koi in a koi pond is to add a clay to our pond on a regular basis, bringing a little of the Niigata mud pond conditions back to our own garden pond.
What do clays do?
Basically speaking, clays behave like an ion exchange material, releasing and adsorbing ions in pond water. Their performance in this role depends greatly on the type of clay used (which is a function of its microscopic structure)
Clay particles are microscopic plate like crystals and that are loosely held together in sheets that may form into stacks. The sheets are able to slip and move over each other (which gives clays the silky smooth texture when rubbing a wet clay between your fingers). Clays are formed by the weathering of other materials, eventually being laid down as a new clay deposit. For example, when the hard granite mineral feldspar is weathered, it produces a clay called kaolinite. Whereas weathered volcanic ash will form a montmorillonite clay. These two clays will behave very differently in water as a result of their very different microscopic structures. Montmorillonite proving to be more effective in a koi pond than kaolinite.
Because of the greater spacing between the montmorillonite sheets (compared with the kaolinite sheets) montmorillonite clays are able to carry a greater number of ions on their surface and are consequently better at remineralising a koi pond.
Because of its mineral make-up, clay particles are typically negatively charged. This means that they attract positively charged ions which will remain closely attracted to each clay particle to be released into the pond water.
It you can see this in action by carrying out the following simple experiment.
1. Take a beaker of de ionised water. pH 7, GH 0
2. Add a remineralising clay
3. Re-test the pH and GH. You will notice that both the pH and GH will increase. When a clay is added to a pond, it will do this on a larger scale.
When a clay is added to a pond, to be as effective as possible it must remain suspended in the pond for as long as possible. This allows ion exchange to take place for a longer period. As you will see from the Niigata mud ponds, the clay particles are so fine that they do not settle but remain permanently in suspension. The same should be true of a clay the you add to your own pond. If it settles out of your pond too quickly and the water soon returns to its crystal-clear state, then it will not have been as effective as a mud pond. A clay should remain suspended for a lengthy period, and as a result will have an ultra-fine particle size. Ultra-fine clays may be hard to mix into a suspension when preparing them, but they remain suspended for longer periods in a pond.
Clays do not dissolve, so once they can no longer be seen in your pond, their effect on water quality will be minimal.
4. Protein Skimming
As pond water ages and the water starts to accumulate dissolved organic carbon compounds (DOC) that discolour the water, the pond will benefit from a protein skimmer.
Protein skimming works by a process called adsorption (not to be confused with absorption) which is the attraction of DOC onto a suitable surface. The process takes advantage of the physical nature of DOC molecules, and something that is all too evident on a foaming pond. DOC molecules cause a foam to form as the molecules which collect at the pond surface cause the pond water to form very stable bubbles. These bubbles remain and form into a foam.
Imagine each DOC molecule to be shaped like a matchstick that behaves with a dual personality. The head likes to be immersed in water (hydrophilic) and will always be wet while the tail end hates water (hydrophobic) and is repelled away from water (see Figure 1). As soon as a bubble forms, these bipolar molecules are attracted to the surface between air and water and accumulate around the surface of the bubble, with the heads pointing outward and the tails pointing inward. This gives the bubble some stability and will resist bursting for some time. Those of us who periodically see a foam on the surface of our ponds are actually observing this chemical phenomenon which is evidence of a high DOC level in the water.
Protein skimming capitalises on the dual personality of the dissolved organic molecules and involves creating a fine mass of bubbles, encouraging the DOC molecules to create a stable foam. The foam then naturally rises above the water surface, collecting in a chamber which requires either manual emptying or is fitted with a drain to waste. When a protein skimmer is first installed, phenomenal quantities of foam (and the final brown liquid) are first formed as the DOC molecules are attracted en masse to the air/water interface. Over time, as the DOC concentration drops, so does the rate at which the foam is formed and liquid ‘protein’ removed. When run continuously, once it has cleared the residual problem, it should keep on top of any subsequent DOC accumulation.
As water passes from our tap, into our koi pond where it circulates for several weeks and is then discharged during a partial water change, it will experience different chemical processes. Having covered the basics of pond chemistry in the previous article, let’s take a look at some of the chemical interactions water may experience on its journey through a koi pond.
1. Water Purifiers
The vast majority of us depend on tap water as the source of the pond water in which we keep our koi.
It is standard practice for water companies to add certain additives to water to make it safe or better for human consumption (chlorine, fluoride) where as our koi demand water with as few additives as possible. Our water companies have a legal responsibility to provide us with water that is safe to drink. They do not however have the same duty of care for our fish’s requirements, and it is our responsibility to take what is suitable for humans, and with a purifier, make it more suitable for our koi.
Time for a little more chemistry.
Water and the solutes dissolved within it are made up of ions. Ions are atoms that are electrically charged and are commonly the building blocks for other molecules. Their charge may be positive or negative, depending on the type of ion, with every ion having a charge which cannot change. In electrolysis, which involves the use of two oppositely charged electrodes (negative and positive) to separate out ions in a solution, the positive electrode is called the anode and the negative electrode is called the cathode. Consequently, negatively charged ions are attracted to the positively charged anode (and are therefore called anions), where as the positively charged cations are attracted to the negative cathode.
For example, if salt (sodium chloride) is put into water, it dissolves and then dissociates into two separate ions – a positive sodium ion (or cation, Na+), and a negatively charged chloride ion (or anion, Cl-). So in solution, sodium chloride no longer exists and it’s ions are free to move and combine with other ions of an equal and opposite charge.
Consequently, all ions can be split into two groups; the positively charged cations such as calcium, magnesium, sodium, iron (all metals) and the negatively charged anions such as bicarbonate, carbonate, chloride, sulphate, nitrate etc.
Fortunately, the vast majority of impurities and inconsistencies between our tap water and that of pure water are due to an excess of specific ions. And as these ions will either have a negative or positive charge, with a little applied chemistry, we can target and remove these offending ions using a water purifier before they enter the pond.
______________
BOXOUT: What is the difference between absorption and adsorption?
A sponge absorbs water into the inside of it’s porous structure. Ion exchange resins are not porous and so we describe the action by which they attract and retain ions on to their surface as adsorption.
__________________
What is ion exchange?
Ion exchange is a reversible chemical process in which the specific ion (such as sodium, Na+) are released from the insoluble solid medium (which is the ion exchange resin) and exchanged for none-desirable or target cations such as heavy metals. There are two types of ion exchange that can be caused to occur within a water purifier; that which removes target cations and that which removes target anions.
How cation exchange works.
Cation exchange resins are usually made from an inert compound called polystyrene-divinylbenzene which is heated in its manufacturing process with concentrated sulphuric acid, causing a sulphonic group (SO3-) to be permanently fixed on to the structural chemistry of the resin beads. Because these sulphonic groups have a negative charge, they can be charged with positively charged ions (cations) typically sodium (Na+), potassium (K+) or even hydrogen (H+). When tap water containing dissolved cations (such as heavy metals) pass by the resin, then these are exchanged for, and trade places with the loosely held sodium ions on the resin. There will come a time when no more cations can be removed by a fully reacted resin which is then described as being ‘exhausted’, and which must then be replaced. The better a resin is protected by pre-filtration from fouling contaminants such as iron and chlorine (which can actually cause the resin polymer beads to disintegrate), the longer it’s active life will be. Cation exchange resins will remove most metallic, positively charged ions such as barium, cadmium, copper, iron, manganese, zinc, calcium and magnesium.
This leaves the negatively charged contaminants or anions which must then be removed before the water can be used to fill a koi pond.
How anion exchange works.
Anion exchange units use a different resin that works in the opposite way to a cation exchange resin. It is charged with either chloride (Cl-) or hydroxyl (OH-) ions, which will then be released into the pond water in exchange for the less desirable contaminant anions. Anion exchange removes nitrates, sulphates and other negatively charged ions.
2. Zeolite
Zeolite is an off-white clay-like mineral that has desirable chemical adsorbing properties. It’s use in the koi world is as an ammonia adsorbing substrate that should be used as a short-term remedy for peaks in ammonia brought about by overstocking, overfeeding or filtration problems. As a means of chemical filtration zeolite should be placed as late in the filtration process as possible. Its porous nature makes it very liable to clogging, and it’s efficiency declines greatly if it is allowed to do so.
Zeolite works by itself being slightly negatively charged, bonding loosely to sodium ions which attach to its surface. In the presence of the ammonium ion (NH4+), ammonium ions become adsorbed to the zeolite in exchange for the sodium ions which are released into the water.
Zeolite has a limited effective lifespan, where its ammonia adsorbing properties decline over time. At such a time, it should be removed to be ‘recharged’, rejuvenating its useful properties so it can be used again. Zeolite can be recharged by placing it in a bath of salt water for 24 hours. The ammonia is released into the water and the Zeolite is ‘recharged’ with the sodium ions; ready for use once again.
Ideally, there should not be a call for Zeolite to be used in a koi pond that is managed wisely. It is only required during an ammonium crisis, which if one occurs, can soon be remedied by stopping feeding and carrying out a partial water change, saving on considerable expense.
3. Clays
It is widely recognised that koi exhibit their best health, colour and vitality when they are kept and reared in a clay pond (often referred to as a mud ponds). In fact mud ponds are a Niigata koi breeders’ key resource for producing the world’s finest koi. These ponds are cut out of clay-rich earth, forming a naturally watertight and mineral-rich base on which to grow koi. The water is highly turbid as koi forage in the muddy substrate, stirring up the ultra-fine clay particles, keeping them in suspension.
We keep koi in highly filtered clear water ponds for our benefit, so that we can see them in all their resplendent glory. But by doing so, we are making a compromise between what we want and what is best for our koi. One way of improving the quality of life for our koi in a koi pond is to add a clay to our pond on a regular basis, bringing a little of the Niigata mud pond conditions back to our own garden pond.
What do clays do?
Basically speaking, clays behave like an ion exchange material, releasing and adsorbing ions in pond water. Their performance in this role depends greatly on the type of clay used (which is a function of its microscopic structure)
Clay particles are microscopic plate like crystals and that are loosely held together in sheets that may form into stacks. The sheets are able to slip and move over each other (which gives clays the silky smooth texture when rubbing a wet clay between your fingers). Clays are formed by the weathering of other materials, eventually being laid down as a new clay deposit. For example, when the hard granite mineral feldspar is weathered, it produces a clay called kaolinite. Whereas weathered volcanic ash will form a montmorillonite clay. These two clays will behave very differently in water as a result of their very different microscopic structures. Montmorillonite proving to be more effective in a koi pond than kaolinite.
Because of the greater spacing between the montmorillonite sheets (compared with the kaolinite sheets) montmorillonite clays are able to carry a greater number of ions on their surface and are consequently better at remineralising a koi pond.
Because of its mineral make-up, clay particles are typically negatively charged. This means that they attract positively charged ions which will remain closely attracted to each clay particle to be released into the pond water.
It you can see this in action by carrying out the following simple experiment.
1. Take a beaker of de ionised water. pH 7, GH 0
2. Add a remineralising clay
3. Re-test the pH and GH. You will notice that both the pH and GH will increase. When a clay is added to a pond, it will do this on a larger scale.
When a clay is added to a pond, to be as effective as possible it must remain suspended in the pond for as long as possible. This allows ion exchange to take place for a longer period. As you will see from the Niigata mud ponds, the clay particles are so fine that they do not settle but remain permanently in suspension. The same should be true of a clay the you add to your own pond. If it settles out of your pond too quickly and the water soon returns to its crystal-clear state, then it will not have been as effective as a mud pond. A clay should remain suspended for a lengthy period, and as a result will have an ultra-fine particle size. Ultra-fine clays may be hard to mix into a suspension when preparing them, but they remain suspended for longer periods in a pond.
Clays do not dissolve, so once they can no longer be seen in your pond, their effect on water quality will be minimal.
4. Protein Skimming
As pond water ages and the water starts to accumulate dissolved organic carbon compounds (DOC) that discolour the water, the pond will benefit from a protein skimmer.
Protein skimming works by a process called adsorption (not to be confused with absorption) which is the attraction of DOC onto a suitable surface. The process takes advantage of the physical nature of DOC molecules, and something that is all too evident on a foaming pond. DOC molecules cause a foam to form as the molecules which collect at the pond surface cause the pond water to form very stable bubbles. These bubbles remain and form into a foam.
Imagine each DOC molecule to be shaped like a matchstick that behaves with a dual personality. The head likes to be immersed in water (hydrophilic) and will always be wet while the tail end hates water (hydrophobic) and is repelled away from water (see Figure 1). As soon as a bubble forms, these bipolar molecules are attracted to the surface between air and water and accumulate around the surface of the bubble, with the heads pointing outward and the tails pointing inward. This gives the bubble some stability and will resist bursting for some time. Those of us who periodically see a foam on the surface of our ponds are actually observing this chemical phenomenon which is evidence of a high DOC level in the water.
Protein skimming capitalises on the dual personality of the dissolved organic molecules and involves creating a fine mass of bubbles, encouraging the DOC molecules to create a stable foam. The foam then naturally rises above the water surface, collecting in a chamber which requires either manual emptying or is fitted with a drain to waste. When a protein skimmer is first installed, phenomenal quantities of foam (and the final brown liquid) are first formed as the DOC molecules are attracted en masse to the air/water interface. Over time, as the DOC concentration drops, so does the rate at which the foam is formed and liquid ‘protein’ removed. When run continuously, once it has cleared the residual problem, it should keep on top of any subsequent DOC accumulation.
