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NanoReefNovice

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NanoReefNovice

I have a dual carbon R/O DI filter that i estimate using 25 gal a week. Havent changed any of the filters in 3 years. I have a milwakee 802 TDS meter that i regularly calibrate. It still reads 0TDS out the filter. Tap water is pretty good at 60 TDS at a 0.68 conversion factor. Qustion is: Should i change the 3 year old filters even though im reading 0 TDS or should i wait. Thanks.

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I have a dual carbon R/O DI filter that i estimate using 25 gal a week. Havent changed any of the filters in 3 years. I have a milwakee 802 TDS meter that i regularly calibrate. It still reads 0TDS out the filter. Tap water is pretty good at 60 TDS at a 0.68 conversion factor. Qustion is: Should i change the 3 year old filters even though im reading 0 TDS or should i wait. Thanks.

 

Out of curiosity have you tried testing it with a different meter? Not to say your meter is bad or anything, just kinda doube checking your work per se.

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NanoReefNovice

Yea i have a ####ty HM one that corresponds with my good meter. But i know what your saying, I never like to trust any measurement... lol

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The prefilter and carbon have very little to absolutely noting to do with TDS, their job is to protect the RO membrane from suspended solids, particulates and colloidal materials and chlorine. The RO membrane and DI resin remove the TDS or dissolved solids, thos that are many times smaller than the prefilter and carbon are capable of. Dissolved solids are in the 0.0001 micron range, prefilters are in the 0.5 to 10.0 range.

 

All that being said you are 2.5 YEARS past due on filter replacements and disinfecting your system.

By waiting as long as you have you may have compromised the membrane and could possibly be growing bacteria and viruses inside the housings and may have slime on the membrane. I would completely disassemble the system, then clean and inspect everything well before installing new filters. Before you do test your tap water and RO only water with the TDS meter, you may be relying on the DI resin to make up for a compromised RO membrane. With your low TDS it can be hard to tell if you don't keep up with the three TDS tests on a regular basis.

 

What are you referring to when you say a 0.68 conversion factor?I can only assume you are talking about the Osmotic pressure, temperature correction and pressure correction factors like this example here:

http://www.spectrapure.com/CALC-FORMULA.pdf

 

Which really doesn't tell us anything except you ahve low pressure and/or low temperature water.

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NanoReefNovice

Thanks for the info. I just figured if it aint broke dont fix it. I was waiting for a rise in TDS to change filters but that hasn't happened. Im getting 0 TDS through the R/O filter before the DI as well. New filters are not cheap so i was hoping i could get away w/o changing them.

 

When i said .68 conversion factor the was referring to the factor my meter uses to calculate TDS, as TDS is a calculation of EC and different meters use different factors.

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When converting EC to TDS you must also take water temperature into consideration. Its not a straightforward conversion.

 

Change the filters, they have no effect on TDS but they will extend or preserve the life of your RO membrane.

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NanoReefNovice

I normally take all readings in EC b/c there is not discrepancies in TDS conversions My meter reads EC and TDS and uses .68 as its conversion factor. I just gave EC as a TDS number b/c i know most people talk in TDS. My meter has ATC and when i calibrate it i take the temp of the calibration solution with a mercury glass thermometer and use a chart. But just to be clear my meter reads 0 µS (EC microsiemen)

 

So your saying change the carbon filters and not the r/o membrane?? How often is one supposed to change carbon filters and r/o filters. thanks!

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The prefilter and carbon should be replaced every 6 months regardless of usage and it is wise to disinfect the system at that time. It only takes a few minutes and can be a lifesaver. Depending on the quality or the prefilter and carbon filters and how well you keep up with replacements the RO membrane should last 18 months to over 10 years. The DI resin replacement is entirely dependent on the quality of the RO water, how much you make and if you have dissolved CO2 present in your treated water. A quick non-scientific rule of thumb says somewhere between 3000 and 6000 total TDS per 16 oz of good quality mixed bed resin. So if your RO only TDS is 3 going in to the DI you can expect 1000 to 2000 treated gallons of water before the DI exhausts. It only a rule of thumb but is pretty reliable.

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NanoReefNovice

Thanks again for the info. I going to go ahead and change out the carbon and sediment filters. What do you mean when you say disinfect the system?

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I have posted the disinfection instructions many times, you should be able to search it easy enough. Basically you disconnect the membrane and soak the remaining empty housings in a diluted bleach solution.

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