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Buckeye Hydro
10/27/2009, 05:53 AM
We've received a lot of questions lately re this topic so I thought I'd post this text from one of our newsletters:

Did you Remember to Flush?

You heard it many times as a child, and may have repeated it to your own children: “Did you remember to flush?” When the question is posed to hobbyists following the installation of new filters, too often the response is “No.” In this article I discuss the purpose of flushing common types of new pre-filters, RO membranes, and DI resin, and describe some procedures to simplify and expedite the procedure.

In general, the process of flushing new filters removes unwanted substances added purposefully to the filters, as is the case in preservatives added to some RO membranes; or unwanted remnants of the manufacturing or shipping process. If not removed from the water purification system, these substances can degrade the function of other filter stages and adversely affect the quality of the water produced. The need for flushing at the time of installation can apply to sediment filters, granular activated carbon (GAC) filters, carbon blocks, membranes, and DI resin, as well as a wide variety of specialty filter cartridges not addressed in detail here.

Sediment Filters
Melt-blown (standard or depth cartridges) or string-wound polypropylene filters, more commonly called “poly filters,” are the most common sediment filters used in the aquarium hobby. Polypropylene is an ideal material for this purpose, and is the material of choice for a number of other components in the water purification trade. Other materials commonly present in sediment filters include polyester, cellulose, and urethane. Depending upon the configuration of the cartridge, surfactants, binders, or adhesives may be used during the manufacturing process. Although flushing is usually not required for polypropylene filters, follow the label instructions in this regard.

GAC Filters
Granular activated carbon, otherwise known as GAC, is a product widely used in the aquarium hobby. This media is commonly manufactured from coal or coconut shell, and has the appearance of small sand-like or larger grains. Very fined-grained carbon dust often accompanies GAC as a byproduct of the manufacturing process, and results to a lesser extent from the handling and shipping of GAC. It is this dust that can be removed by flushing. GAC axial-flow (end to end) filters often utilize plastic housings and end caps, and rubber compression gaskets.

Carbon Blocks
Carbon blocks are composed of activated carbon which is ground to a powder and formed into a tube in an extrusion or historically, a molding process. The process of forming a very fined-grained powder into a tube requires the addition of a binder to hold the particles together. End caps are adhered to the ends of the carbon tube. Carbon blocks don’t release appreciable amounts of carbon dust relative to GAC; however they should be flushed at first use to remove dust and remnants of binders used in manufacturing.

Reverse Osmosis Membranes
Perhaps the most widely used membranes in the aquarium trade are the TW-1812 products made by Filmtec, a subsidiary of the DOW Chemical Company. These membranes are typically sold dry, sealed in a plastic bag. Some membranes are sold “wet” – these membranes have been tested by the manufacturer, preserved in a solution containing a preservative, and sealed in plastic. Filmtec recommends that both the dry and wet membranes be flushed to remove the preservative solution, as well as any other substances remaining on the membranes from the manufacturing process.

Deionization Resin
The final stage in many point-of-use systems used in the marine aquarium hobby of course, contains deionization (DI) resin. When installing a new DI resin cartridge, the resin should be flushed to remove any residual substances from the manufacturing process, as well as broken beads/fines. The flushing should consist of two to three bed volumes of water – that is, two to three times the volume filled by the resin. The volume of a standard 10 in. x 2.5 in. resin cartridge is approximately 0.2 gallons, so a 0.6 to 1 gallon flush is sufficient.

How best to flush new filters? Follow a few simple guidelines and you’ll have the filter in place in no time.

No. 1: Identify the amount of water in gallons or minutes needed to flush the filter (see recommendations above), or refer to instructions that come with your filters.

No. 2: Avoid passing flush water into other filter stages. It is inadvisable for example, to install a new GAC cartridge in Stage 2 of a multi-stage system and have the carbon fines flushed out of the GAC only to be trapped by a carbon block in the next stage.

Two approaches are commonly employed here, depending upon the configuration of your water purification system. In systems with a flush valve (flow restrictor bypass valve), the filter to be flushed can be placed in the housing immediately prior to the RO membrane housing, and can be flushed with the flush valve completely open. A much better approach, which avoids exposing the RO membrane to flush water, is to place the filter to be flushed in the final (post-RO membrane stage normally occupied by a DI resin cartridge. In this case, flush water immediately exits the system after passing through the new filter.

Regardless of which approach to flushing you implement, never expose a Thin Film Composite RO membrane to chlorinated water. Remember that an activated carbon prefilter stage is required to remove chlorine from tap water. Nearly all RO and RO/DI systems in use in the marine aquarium hobby today utilize TFC membranes. A sure indication your system utilizes a TFC membrane is the presence of a GAC or carbon block prefilter.

Russ @
Buckeye Field Supply