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Join Date: Nov 2003 Location: North Carolina
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 Add yours! |  Source Water Discussion
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Originally Posted by Leebca There may be some concern about the quality of the water added to the artificial salt for use in a marine aquarium, water used to compensate for evaporated water, and the use of natural sea water. Let's agree on some definitions Source water - This is the water used to make up marine water from artificial salts. NSW - This is the acronym for natural sea water. DI - This is the acronym for deionized water. Simply, deionized water is water that has had ions removed from it. RO - This is the acronym for reverse osmosis. Water is forced through a membrane that strains out many large molecules of impurities. RO/DI - The combination of RO and DI. Usually impure water first passes through the deionization treatment then is forced through the RO membrane. ----- There is no doubt that the best source water that can be used is distilled water. However, that is expensive on a large scale and, for other than an marine systems under 25 gallons, isn't too attractive. Even though the bottle you see in the store is marked "distilled water" doesn't mean it is pure. If the equipment used for the distillation process was metal, then there is a chance the "distilled water" may have dissolved metal in it. The best distilled water has been distilled using equipment made of glass or other inert material. It was and still in some places, common to use copper stills to make distilled water. However, in the USA most distilled water is prepared using equipment made of inert material and the water is very pure. ------- Another grade of water is DI water. Deionized water means just that ions are removed from the water. This is usually done by a resin. Resin in a tank is held in place while water passes through it. This is called a resin bed. The resin beads take on ions and release another, harmless or preferred ion. It is a displacement action. There are two concerns: what ions are being removed and what is replacing those ions. There are positive and negative unwanted ions (cations and anions) to get out of untreated water. Resins usually only deal with one or the other ion. To remove both positive and negative contaminating ions from water, two resin beds are needed or a mixed resin bed of these two kinds of resins, is needed. With two resins most of the unwanted ions are removed. What is often replaced into the water is an acid or base. Deionized water has to be watched for pH. However, what isn't removed by this process is organic chemicals. If the resin removes only ions then what is left are the chemicals will little or no chemical charge to them. They get through the resin bed. -------------- Another water treatment is RO. Reverse osmosis is where water is forced onto a membrane that has tiny, unseen holes in it, like a filter but on a molecular level. What passes through the membrane is very small molecules (like water, ammonia, ions, cations, etc.). This treatment is very good at separating large molecules, like proteins and fats, from the water being forced through it. Usually this process requires the flow and force of water against the membrane. Some water is lost by passing by the membrane taking with it the molecules that wouldn't pass through the tiny holes. This process wastes some water. Water up to 75% or more can be wasted making RO treated water. That is, for every gallon of RO water made, it took up to 4 gallons of water to feed the treatment system. There are more or less efficient RO units available, but all waste some water. The next grade of source water is RO/DI water. It is desirable for most medium to small marine systems, but the RO portion of the treatment does waste water. It may take up to 4 times the water to get 1 part of RO water. Thus, up to 3 parts may be wasted in the sense that it goes down the sewer/drain. What isn't removed by this process are very small ions and molecules. In order to let the water molecule go through the membrane, then other molecules of that or smaller in size will also pass through the membrane. ------- A combination of RO/DI is another grade of water. If you've read the above two descriptions, you'll see that DI won't remove large organic molecules and RO will prevent large molecules from passing through the membrane. The combination of these two treatments (using two resins) leaves water without ions and large organic molecules. DI water is usually sent to the RO membrane for final polishing. However still what remains is small organic molecules, like ammonia or small molecules of other organics. ---------- Then there is activated carbon treated water. That removes organics. Put activated carbon behind a two resin treatment followed by reverse osmosis and you have very clean water. ------------- Measuring quality The above treatments of tap water still pose some exposure and risk that contaminants may get through the system that are undesirable for marine livestock. Two primary concerns: 1) It is still worthwhile to verify the total dissolved solids (TDS) left in treated water and 2) to test for ion ingredients, on a regular basis. The aquarist can check the TDS of water with a TDS meter. They are usually less than $80. and can be found cheaper. The TDS of distilled water is 0.0 ppm. Keeping in mind the accuracy and reliability range, a TDS meter may have a range of results and still be reliable in a sense. These meters usually need calibration. The TDS of RO/DI water should be below 10. ppm. Rarely does this water make it below 2 ppm, with the average being around 5-6. Besides monitoring TDS to verify the RO/DI treatment system is working properly, the aquarist may wish to test for small ions (iron, copper, etc.) in the water to verify these are not finding their way into the aquarium. pH cannot easily be measured in water with a low concentration of ions. Ions carry the electric charge which measures the pH. After performing a TDS measurement, add some table salt to the water and test for pH. Polishing A third concern is organic materials. A good RO unit will prevent large dissolved organic molecules from slipping through, but can miss some organic gases. Still it doesn't hurt and is recommended to follow the RO/DI treatment with a chamber of activated carbon to polish any residual (organic gas, and ionic) components. The TDS of this water is usually below 2 ppm when the two different types of deionizing resins are used. Untreated water problems The lowest grade of untreated water is often well water followed by tap water. Even if the aquarist tests that water for impurities commonly monitored in the marine aquarium (e.g., phosphate, nitrites, nitrates, ammonia, silica, iron, etc.) there is no way for all impurities to be tested. Anything can be in the water that is not harmful to humans but harmful to marine livestock. There are test kits to test for pesticides and other contaminants (e.g., the Watersafe All-In-One Drinking Water Test kit), but still these tests don't cover the entire range of impurities harmful to marine livestock. Another concern is the wide range of water quality from municipalities and different sources (e.g., well water, water table, lakes, etc.). The reader should refer to this reference for more information on tap water concerns: Chemistry and the Aquarium For all tense and purposes, source water as defined above is never well water, nor tap water. NSW Natural sea water would seem to be the best choice for water changes in the marine system. However, where can it be gotten free of human pollution? Much of the USA coastal areas are polluted. NSW shares a common concern with tap water purity in that the aquarist can't test for everything that might be in the water. There is some minimal exposure to acquiring disease and undesirable organisms through the use of NSW. I would not be concerned about this, however. I've tested (analytical chemical analysis) NSW that was sold as 'not polluted.' I have found petroleum and fuel products in some of them. A rather humorous event was a person who went 25 miles out to sea and collected water in vats. The vat water showed petroleum products that matched those used by the boat. The person literally brought their own pollution to a relatively clean, unpolluted area of the ocean. This points out the need to control how the water is collected even if it is clearly done in a non-polluted part of the ocean/sea. This is not a recommendation to not use NSW. Just a recommendation to be wary of what can go wrong that the average aquarist is unable to verify by home test kits. Recommendation Choose your source water and NSW with consideration to the purity you need; the cost; value; the environmental impact (wasted water); the quality of water in your area/the quality of water you have to start with, and exposure and risks to impurities. All this leads to the final questions: How pure does the water need to be for a reef aquarium? How clean is clean enough? These are good questions that can’t be always answered just one way. Don't ignore the one very important variable in all of the above. The variable is what kind of water quality is coming into the treatment system. What kind of untreated water is being treated. If it contaminated well water, the best treatment may still leave undesirable chemicals in the water, unsuitable for reef inhabitants. The quality of water produced is also related to the location the aquarist is, within the USA. Different parts of the country have different water quality issues. In general, there is a good argument that, for "normal" tap water, without pesticides and unusual contaminants, a dual resin bed (one resin to remove positive ions and one resin to remove negative ions) treatment followed by activated carbon is adequate for reef systems and FOWLR systems. Personalized Systems What source water or water do you use for your marine tank water changes? For your top-off or evaporated water replenishment? Please post your experience and what you use. I use RO/DI (one kind of resin) and activated carbon for the source water for my FOWLR system. This relates to the very heavy handed quantity of cations in the tap water coming through to my home. My final TDS is below 6 ppm.
__________________ LEE |
Last edited by Woodstock : 07-16-2008 at 04:13 PM.
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07-16-2008, 01:41 PM
Neither RO nor DI will take out CO2, which can kill your DI. We see this often in "well" water. In short, the CO2 will combine with OH- from the resin or CO2 will combine with water to give H2CO3, which then dissociates to HCO3- and H+
