Most marine aquarists would agree that reverse osmosis (RO) water is the optimal type of water to be used in creating (mixing) the SW used in your marine tank. For most of us, tap water and even rain water is quite impure. Hobbyists who use straight tap water may face higher than normal levels of copper if one lives in a house that has copper pipes; you may have nitrates if you live in an agricultural area that uses fertilizers that leech into the groundwater; or, you may have excess levels of heavy metals which could build up over multiple water changes.
A reverse osmosis filter creates 'pure' water by using a semi-permeable membrane to filter out various minerals and contaminants. In actuality, the water isn't 100% pure but can come quite close when a deionizer filter (DI) is added on. This uses a resin to bind up any remaining ionized contaminants. So, you are standing there with your orange Home Depot bucket filled with RO water. How do you know how pure it is?
What are Total Dissolved Solids?
Total dissolved solids (TDS) are the total solids dissolved in water that are not water molecules. This includes minerals, metals and ions. Note that this is dissolved solids. There may be undissolved solids in suspension, such as particulate dust. TDS are measured in parts per million (PPM) which is a measure of weight against water.
How Do you Measure Them?
A TDS meter should be 'standard equipment' for those who choose to use an RO filter to make their SW. The meter uses the electrical conductivity of water to determine it's purity. Pure water obviously has virtually no electrical conductivity. Therefore, the amount of 'contamination' by cations and anions can be read by a TDS meter. There are equations to calculate this out which you can research. Typically, the meter has 2 prongs which, when placed in your RO sample, will give a read out on the LCD screen.
What Filtration Methods Remove TDS?
Typically, there are four main ways to remove TDS:
Photo of my six stage RO/DI filter. 1) indicates the three initial pre-filters for removing larger molecules and particulates. 2) indicates the RO membrane. 3) indicates the DI resin filter. The smaller un-numbered filter on the top is a coconut shell filter added for flavor and is disconnected on my filter as it can increase the TDS.
Why is Measuring TDS Important?
There are many reasons to measure TDS in the real world but with regards to our aquariums, there are mainly two:
Hope this helped.
SH
A reverse osmosis filter creates 'pure' water by using a semi-permeable membrane to filter out various minerals and contaminants. In actuality, the water isn't 100% pure but can come quite close when a deionizer filter (DI) is added on. This uses a resin to bind up any remaining ionized contaminants. So, you are standing there with your orange Home Depot bucket filled with RO water. How do you know how pure it is?
What are Total Dissolved Solids?
Total dissolved solids (TDS) are the total solids dissolved in water that are not water molecules. This includes minerals, metals and ions. Note that this is dissolved solids. There may be undissolved solids in suspension, such as particulate dust. TDS are measured in parts per million (PPM) which is a measure of weight against water.
How Do you Measure Them?
A TDS meter should be 'standard equipment' for those who choose to use an RO filter to make their SW. The meter uses the electrical conductivity of water to determine it's purity. Pure water obviously has virtually no electrical conductivity. Therefore, the amount of 'contamination' by cations and anions can be read by a TDS meter. There are equations to calculate this out which you can research. Typically, the meter has 2 prongs which, when placed in your RO sample, will give a read out on the LCD screen.
What Filtration Methods Remove TDS?
Typically, there are four main ways to remove TDS:
- Carbon Filtration: Carbon has a large surface area and will adsorb large molecules and also mechanically filter out larger particulate undissolved solids.
- Reverse Osmosis: As we all know by now, water under high pressure is forced through a semi-permeable membrane which allows water to pass through and traps larger ions. This is the workhorse area of the filtration system.
- Deionization: This filter utilizes a resin material which will bind most residual ions in the final water from the RO membrane.
- Distillation: This is straight forward: water is boiled and the water vapor without contaminants is condensed and recollected as pure.
Photo of my six stage RO/DI filter. 1) indicates the three initial pre-filters for removing larger molecules and particulates. 2) indicates the RO membrane. 3) indicates the DI resin filter. The smaller un-numbered filter on the top is a coconut shell filter added for flavor and is disconnected on my filter as it can increase the TDS.
Why is Measuring TDS Important?
There are many reasons to measure TDS in the real world but with regards to our aquariums, there are mainly two:
- to test the purity of your water sample
- to test your water filter and troubleshoot the system if your TDS rises; to determine when your RO membrane needs replacement
Hope this helped.
SH
