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8.13.3 DEIONIZERS:
Deionization by means of 2 separate treatment columns, one with cation resins and the other one with anion resins is another very efficient way of pretreating your tap or well water. Alternatively hobbyists can use a single column unit in which the bed of resins is already mixed. The latter are normally less pricey than double type units. They are, however, more difficult to recharge or regenerate.
Good deionizers remove all the pollutants that the hobbyist needs to remove before using such water and operate at degrees of efficiency as good as reverse osmosis units.
You must flow water slowly through the resins to increase the contact time, and to attain the highest cleansing possible. 20 to 30 gallons per hour is better than higher velocities, although many units will still operate relatively efficiently up to velocities of 1 gallon per minute, or 60 gallons per hour.
Although some resins leached phenols in the water a number of years ago, this problem has now been resolved, and all units that I have tested, using resins from Dow Chemical and Rohm and Haas, are now safe. Because of the very large number of resins, and the great disparity in the price of such resins, it is important to buy your deionizer from a company that has experience with them, has tested many resins, and can service your unit if need be. The latter is most important.
Some resins may cost only around $100.00 per cubic foot at the distributor level, whereas others may cost around $600.00. You can well imagine that a company using the latter will have to get more money for their units than one using the former. It should also be clear that the more expensive resins do a much better job at cleaning up the water than the industrial type, inexpensive ones.
As the resins inside the deionizer unit polish the water that flows through the columns, they load themselves progressively more and more with impurities. A point will soon come where the resins are saturated and need to be cleaned, so they can be reused effectively.
The more resin you are using the longer if will take for this to happen; the purer the water to be treated the longer this will take to happen; the more loaded with impurities the water to be treated is, the sooner it will be necessary to recharge your deionizer. Cleaning resins of impurities is called regeneration or recharging. This is not an easy process and it requires the use of several chemicals. One for each type of resin. The most frequently used chemicals are hydrochloric acid and sodium hydroxide, both usually in 4% or 5% solutions.
In mixed bed resin deionizers the resins need to be separated before the treatment can begin, making the regeneration process yet a little more difficult. Separating the resins is usually done by blowing air mixed with water from the bottom to the top of the column. Because the two types of resins have different weights, one is much lighter, the action of the water and air mix will tend to make the lighter resin migrate to the top. This top layer can then be separated from the bottom one, and both resins can now be treated independently of each other. In the middle, between the two layers, a small band of mixed resin will remain, and should be treated separately or discarded.
Regenerating is not hard to do, but it does require time and the use of chemicals that must be handled with care. Recharging resins, and using deionizers, is discussed much more extensively in my other book called Small Reef Aquarium Basics and has also been reviewed in many articles in Marine Reef, the newsletter published by Aardvark Press. You may wish to refer to either, or both, for more details.
The advantages of deionizers are:
The two disadvantages that need to be pointed out are that to recharge the unit you must use strong chemicals, and that such chemicals may not always be that easy to obtain, especially not in small quantities.
On the other hand, some companies, for example TAT, offer a recharging service for a nominal fee per year, something that will make the regeneration process a lot easier.
8.13.4 USING ACTIVATED CARBON:
Although activated carbon, for instance acid washed pelleted coconut shell carbon, removes many undesirable compounds from tap and well water, and although it is easy to use, I have not been able to attain the water purity that I find is needed to run a reef tank by using activated carbon on its own to pretreat the water used on my home tank.
Combining carbon filtration with a micron filter, placed before the carbon filter, is one step in the right direction, because such a micron filter will remove particulate matter as well. The lower the micron rating of the cartridge in the filter housing, the better the filtration will be, but the more often you will have to replace that cartridge.
Ideally, one should use a Poly Bio Marine Fin-L-Filter because such filters work at the sub-micronic level and remove bacteria, parasites and other such small life forms as well. Well water often contains many of them. Used on water lines with high input pressure, such filters can treat great amounts of water before the sub-micronic filtering assembly is in need of replacement. Using Fin-L-Filters is as good as cold sterilizing, meaning that the water is completely free of any bacteria etc.
Such a dual set-up, using either micronic or sub-micronic filtration, combined with a third form of filtration: molecular absorption, gives the best results and delivers effluent that can be used directly in the tank. I use such a system myself. A drawing showing how to hook one up can be found elsewhere in the book. Molecular absorption filters use a special form of Poly Filter, in disc form and with a greater absorption capability than the rectangular pads. They are made by the same company: Poly Bio Marine Inc. Although I have absolutely no interest in that company or in their products, I find Poly Filters to be the best of all chemical filtration media presently on the market, and one that every reef keeping hobbyist must use. No ifs or buts.
The advantages of a triple system such as the one just described are multiple:
There are no disadvantages that I can pinpoint. The only remark, in all fairness, is that this system requires the largest initial investment: possibly as high as $450.00, but in the long run it is the one that gives the least amount of problems.
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