What is RO?
- Thread starter dschddny
- Start date
RO stands for Reverse Osmosis.
Osmosis - the diffusion of water across a semi-permiable membrane from a solution of high water concentration to a solution of low water concentration until a state of equalibrium is reached.
It is hard to describe, and I didn't fully understand osmosis until someone hit me over the head with a chemistry book. I still don't know what made me "get it". I think it was just finally being able to picture the process biologically rather than with the steril mechanical examples given in text books.
Think of a freshwater fish. A freshwater fish is composed of cells. Cells are contained by the cell membrane, which, btw, happens to be (ta da) a semi-permiable one. The concentration of salt within a fish's cells is greater than the concentration of salt in the fresh water of the fish's environment. Where you have more salt, you have less room for water, so the amount of water inside the fish is less than the amount of water outside the fish. Water (like all forms of energy) wants to travel from solutions of high concentration to low concentration, so the water from the environment is going to pass through the cell's membrane into the fish's body. The salt, on the other fin, cannot pass through the membrane, hence the semi-permeable aspect of the process. The saying in fish physiology classes are that freshwater fish are always pissing. They are compensating for the constant absorption of water through their cell membranes because there is more water in their environment than actually inside their bodies. If they did not continually piss out the extra water they absorb, their cells will swell up like balloons and burst (a process called lyses), thus killing the fishy.
Now (stay with me here, this is where it gets a bit confusing), on the flip side of the same token, a saltwater fish must always be drinking. If you can figure out why, then you will have a good grasp on the concept of osmosis.
Reverse Osmosis - The process of extracting water from solutions with high mineral/particulate concentrations by using pressure to force it through a semi-permiable membrance against the concentration gradient. The result is pure H2O with no contaminates.
The semi-permiable membrane only allows water to pass. Lets say you have seawater. Now seawater is a whole lot of minerals, and actually very little H2O. If you were to put a pure H2O solution and a seawater solution next to each other with the semi-permiable membrane between them, the pure H2O solution will diffuse into the seawater, diluting the seawater solution. But if you applied pressure to the seawater side, you will force the water through the membrane against the concentration gradient, in essence "squeezing" the H2O from the seawater. What you would have left behind on the seawater side is a concentrated sludge of minerals and particulate matter (yucky). On the other side you would have pure H2O.
RO water should not be used in fish tanks unless it is being mixed with appropriate concentrations of minerals to provide fish with the trace elements they need to function. Using strait RO water is -deadly-. Fish derive many of the trace minerals (Zinc, Calcium, etc) directly from their environment, and RO water lacks these minerals. The advantage to having RO water is being able to mix the tank water chemically to exacting conditions without the concern of added impurities (such as with a reef tank, mixing the RO water with commertial sea-salts so that you do not have the impurities of tap water mixed into your tank).
The process isn't very expensive anymore (judging from the number of home RO units on the market), but it takes something like four to five gallons of what we consider drinking water to produce one gallon of RO water. Personally, I don't like the taste of RO water. Give me contaminates any day.
~~Colesea
Osmosis - the diffusion of water across a semi-permiable membrane from a solution of high water concentration to a solution of low water concentration until a state of equalibrium is reached.
It is hard to describe, and I didn't fully understand osmosis until someone hit me over the head with a chemistry book. I still don't know what made me "get it". I think it was just finally being able to picture the process biologically rather than with the steril mechanical examples given in text books.
Think of a freshwater fish. A freshwater fish is composed of cells. Cells are contained by the cell membrane, which, btw, happens to be (ta da) a semi-permiable one. The concentration of salt within a fish's cells is greater than the concentration of salt in the fresh water of the fish's environment. Where you have more salt, you have less room for water, so the amount of water inside the fish is less than the amount of water outside the fish. Water (like all forms of energy) wants to travel from solutions of high concentration to low concentration, so the water from the environment is going to pass through the cell's membrane into the fish's body. The salt, on the other fin, cannot pass through the membrane, hence the semi-permeable aspect of the process. The saying in fish physiology classes are that freshwater fish are always pissing. They are compensating for the constant absorption of water through their cell membranes because there is more water in their environment than actually inside their bodies. If they did not continually piss out the extra water they absorb, their cells will swell up like balloons and burst (a process called lyses), thus killing the fishy.
Now (stay with me here, this is where it gets a bit confusing), on the flip side of the same token, a saltwater fish must always be drinking. If you can figure out why, then you will have a good grasp on the concept of osmosis.
Reverse Osmosis - The process of extracting water from solutions with high mineral/particulate concentrations by using pressure to force it through a semi-permiable membrance against the concentration gradient. The result is pure H2O with no contaminates.
The semi-permiable membrane only allows water to pass. Lets say you have seawater. Now seawater is a whole lot of minerals, and actually very little H2O. If you were to put a pure H2O solution and a seawater solution next to each other with the semi-permiable membrane between them, the pure H2O solution will diffuse into the seawater, diluting the seawater solution. But if you applied pressure to the seawater side, you will force the water through the membrane against the concentration gradient, in essence "squeezing" the H2O from the seawater. What you would have left behind on the seawater side is a concentrated sludge of minerals and particulate matter (yucky). On the other side you would have pure H2O.
RO water should not be used in fish tanks unless it is being mixed with appropriate concentrations of minerals to provide fish with the trace elements they need to function. Using strait RO water is -deadly-. Fish derive many of the trace minerals (Zinc, Calcium, etc) directly from their environment, and RO water lacks these minerals. The advantage to having RO water is being able to mix the tank water chemically to exacting conditions without the concern of added impurities (such as with a reef tank, mixing the RO water with commertial sea-salts so that you do not have the impurities of tap water mixed into your tank).
The process isn't very expensive anymore (judging from the number of home RO units on the market), but it takes something like four to five gallons of what we consider drinking water to produce one gallon of RO water. Personally, I don't like the taste of RO water. Give me contaminates any day.
~~Colesea
For saltwater, RO is the water of choice. It is (almost) chemically pure so there is nothing added to the water unless it is done on purpose. Salinity, carbonate hardness, and trace elements are easier to control and there is no chlorine, metals, nitrates, phosphates, or silicates in RO water to worry about.