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TDS Meter Readings


LebaneseDlight

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LebaneseDlight

I have a Hanna TDS meter. Not surprisingly, the Los Angeles tap water has around 450 TDS. After my 5 stage RODI, I get 0.01 TDS. Is this something that would concern you? My airwaterice RODI is new (I've made maybe 20 gallons in it).

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AZDesertRat

There are no decimal points in the TDS reading. What appears to be a decimal is actually a power ON indicator. Your TDS is 1 which means it is time to start looking at the RO rejection rate or removal efficiency and your DI condition. I usually order a new DI when I first start seeing signs of anything other than 0 TDS and change it before it starts to read 2 on a consistent basis.

 

You need 3 TDS readings to troubleshoot a RO/DI, tap water , RO only TDS and final RO/DI TDS. Use a squeaky clean, clear glass drinking water glass washed by hand in very hot water so it has no dishwasher soap residue or antispotting rinse agents in it.

Start by taking a tap water sample, insert the meter, take a minute to let the reading stabilize then write it down. Next, very important, triple rinse the glass and TDS meter in RO/DI or distilled water then grab a sample of RO only water before the DI. If you do not have a DI bypass valve you can disconnect the 1/4" line from the RO down to the DI at the DI end to fill the glass then reconnect the line. Again insert the meter, let it stabilize and write it down. Do another triple rinse with RO/DI or distilled and fill the glass with permeate or RO/DI water. Insert the meter, let it stabilize, write it down and do a final triple rinse. Cap the meter and turn the glass upside down so it stays clean for next use.

 

What are your three TDS readings?

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LebaneseDlight

Thanks AZ. I'll have to try this tonight when I get home. I wonder if not Flash Flushing has something to do with it? Maybe it's as simple as my cup isn't as clean as it should be.

 

Also, how do you clean the TDS meter's prongs? Just dip in RO I imagine?

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AZDesertRat

You rinse the meter in RO/DI or distilled water, this is what cleans it. Same with the clear drinking water glass which is used so you can visibly see how clean it is.

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LebaneseDlight

Today the TDS reading was 4 consistently. I don't have a DI cut off valve, however, figured out the issue I was having. I always seem to have oddball issues... I noticed the waste water was not flowing as fast as it had a couple months ago when new. Then I checked under the sink (my RO/DI is installed under my kitchen sink) and saw a fold in the waste water line. I think the waste water was being forced back into the filters or out the good water line. I flushed the water from the membranes and took more readings and they're consistently 0 now.

 

The takeaway: a TDS meter is an invaluable tool.

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nanolutionary

Your TDS is 1 which means it is time to start looking at the RO rejection rate or removal efficiency and your DI condition. I usually order a new DI when I first start seeing signs of anything other than 0 TDS and change it before it starts to read 2 on a consistent basis.

 

Glad you figured out the problem LebaneseDlight!

 

I'm having similar readings of TDS at the moment and could do your with help AZDesertRat.

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AZDesertRat

To troubleshoot a RO/DI you need several pieces of information. Tap water TDS, RO only TDS before the DI and final RO/DI TDS. Water temperature and water pressure. Are you using softened water and if not do you know the calcium carbonate hardness and if it contains any CO2 or not. Exact measured waste ratio and membrane brand and model. A these things help.

Other things that are also good to know are sediment filter and carbon block micron ranges, age of the filters since the last replacement, the age of the membrane and what DI resin or cartridge you are using, how long it has been in service and was it factory fresh when installed or had it been sitting around or stored before being used.

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  • 4 weeks later...
LebaneseDlight

To troubleshoot a RO/DI you need several pieces of information. Tap water TDS, RO only TDS before the DI and final RO/DI TDS. Water temperature and water pressure. Are you using softened water and if not do you know the calcium carbonate hardness and if it contains any CO2 or not. Exact measured waste ratio and membrane brand and model. A these things help.

Other things that are also good to know are sediment filter and carbon block micron ranges, age of the filters since the last replacement, the age of the membrane and what DI resin or cartridge you are using, how long it has been in service and was it factory fresh when installed or had it been sitting around or stored before being used.

 

Hi Az (and anyone else knowledgable on the subject),

 

I'm still having problems with my TDS readings. No matter if I flush for 15 minutes, or take multiple readings, I'm always getting a TDS of 2-4 off my RODI. I'm having a Cyano and Diatom issue (my tank is just over 3 months old) and not sure if these particles on the water are contributing. My Phosphates are around 0.02 but I'm using GFO and GAC.

 

I did some testing today to give you more info. My tap water (Los Angeles) has a TDS of almost 500! My RO only water is reading 17-19. My RO/DI water is reading 2-5. I'm not sure what the pressure is (how do I find out?). And the temp is around 70-75 I would estimate. I'm using a AIRWATERICE Compact 75 GPD Reefkeeper RODI

http://theh2oguru.com/reefkeepers-rodi/compact-75-gpd-reefkeeper-rodi.html. I have made about 50 gallons of RO/DI since purchased 3 months ago.

 

Any help is much appreciated.

 

Greg

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AZDesertRat

With that style of throw away DI you may never reach 0 TDS. The horizontals just don't compare to a real full size 20 oz vertical DI. For one you have no idea how old the resin is in the cartridge since you cannot refill it. Another is they do not hold as much resin so do not last as long even if it were fresh resin and the correct resin blend. Yet another is with horizontals the water takes the path of least resistance along the bottom of the cartridge so you gte poor treatment.

 

One thing you can do that may help is take the horizontal DI off the top and mount it vertically beside one of the other full size canisters so it fills from the bottom and exits the top. In this way all water and resin will come into contact wih each other and you get better contact time.

 

If it were me I would eliminate the redundant, unneeded second carbon block, install a 1 micron or smaller sediment filter in the first canister, a 1, 0.6 or 0.5 micron carbon block in the second then spend a few minutes replumbing the third full size vertical canister into a real DI filter with a refillable cartridge so you can add 20 oz of fresh, reef specific DI resin such as the Spectrapure SilicaBuster. It is very easy to do and only takes a couple $$ and 15-20 minutes to convert then you can buy the SilicaBuster or SuperSilicaBuster DI cartridges and get 0 TDS easily. I would also spend $15 on a inline pressure gauge as pressure is a very impotant piece of troubleshooting a RO/DI system.

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LebaneseDlight

With that style of throw away DI you may never reach 0 TDS. The horizontals just don't compare to a real full size 20 oz vertical DI. For one you have no idea how old the resin is in the cartridge since you cannot refill it. Another is they do not hold as much resin so do not last as long even if it were fresh resin and the correct resin blend. Yet another is with horizontals the water takes the path of least resistance along the bottom of the cartridge so you gte poor treatment.

 

AZ, your RO/DI info to the online reefing community is so valuable - thank you for the quick reply.

 

I just purchased this two stage DI and will replace my horizontal DI http://spectrapure.com/MaxCap-D2-Dual-Stage-DI-System-Add-On-w-SuperDI-Cartridges?filter_name=d2.

 

In a couple months, when time to change the RO membranes, I'll also invent in some of the tweaks you mentioned and Spectrapure membranes.

 

Do you think this is a good plan of action?

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AZDesertRat

Yes.

Your RO rejection rate is (500-19=481, 481/500=.962, .962x100= 96.2) 96% rejection or removal efficiency. That is just OK but could be better especially with the high TDS waters we both see. My TDS is 560-600 and I get a RO only TDS of between 2 and 3 so a better membrane would not only help you get to but stay at 0 TDS for a long time. For every 2% you can improve that 96% you will double your DI life. My rejection rate averages 99.4% so DI lasts a long time even with high TDS tap water.

 

Adding the dual DI is great but a better membrane would make it last much longer and pay for itself in resin savings very quickly if you make much water.

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