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RO/DI, TDS and Chlorine


HM3105

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Hey all,

 

I feel like I know the answer to this question but I'd like confirmation.

 

I have the Mighty Mite with DI added from Air, Water, Ice. Over the last month or so its been causing my water pipes to hum when I run it. I think the temp. dropping is causing the issues. I have found that if I open the the flow restrictor for the waste water line some the humming will stop. I measured the TDS of the RODI water coming out of the system after opening the flow restrictor and it is reading 0.

 

As I understand it, once the water hits the carbon block all the chlorine is stripped out. So I presume if the water is passing through the RO membrane and the DI resin and ending up with 0 TDS the chlorine is also removed. Is that an accurate assumption?

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Check on the TDS values after the RO but before the DI.

 

Water coming from the DI will show 0 TDS until the DI is used up. If the TDS of the water coming from the membrane is higher, you are going to use your DI resin up faster.

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A decent carbon block: http://spectrapure.com/FILTERS-MEMBRANES-RESIN/CARBON-FILTER-CARTRIDGES/0.5-Micron-Carbon-Block-Filter-10-inch (that isn't used up) will remove all the chlorine. The carbon filter has very little to do with TDS.

 

You need the flow restrictor set properly so the membrane provides the optimum rejection rate, without wasting a lot of water. I can't address why your unit is humming. Are the filters new, or are they due to be replaced? Have you considered getting a new unit: http://spectrapure.com/RO-RODI/RODI-SYSTEMS/Refurbished-90-GPD-RODI-System

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Is your faucet or source of water opened completely? If you are trying to adjust flow or pressure using the faucet this is often the problem. Same if you are trying to adjust temperature with the faucet, COLD water only no hot or blending.

 

One issue with the small "portable" systems is they use smaller replacement filters which are not the same micron ranges reefers prefer and do not filter as well nor last as long. The sole purpose of a sediment filter is to protect the billions of tiny pores in the carbons surface and the carbon is to protect the RO membrane from chlorine so it does not melt. Chlorine does not register well as TDS and is at such low levels so I use a low rangle chlorine test kit (Spectrapure)to monitor for chlorine breakthru.

 

As already pointed out, you need to know the TDS of the RO only water before the DI since the RO is where 90-98% of the work is performed. The RO could be doing nothing and the DI is acting as a crutch to make up for it and may not last more than a few gallons before it is exhausted. You also need to keep that waste ratio around 4:1 so you have sufficient pressure for the membrane to work.

 

What is your water pressure at the membrane and what are your tap , RO only and final RO/DI TDS numbers? What is your exact measured waste ratio?

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Check on the TDS values after the RO but before the DI.

 

Water coming from the DI will show 0 TDS until the DI is used up. If the TDS of the water coming from the membrane is higher, you are going to use your DI resin up faster.

 

 

A decent carbon block: http://spectrapure.com/FILTERS-MEMBRANES-RESIN/CARBON-FILTER-CARTRIDGES/0.5-Micron-Carbon-Block-Filter-10-inch (that isn't used up) will remove all the chlorine. The carbon filter has very little to do with TDS.

 

You need the flow restrictor set properly so the membrane provides the optimum rejection rate, without wasting a lot of water. I can't address why your unit is humming. Are the filters new, or are they due to be replaced? Have you considered getting a new unit: http://spectrapure.com/RO-RODI/RODI-SYSTEMS/Refurbished-90-GPD-RODI-System

 

 

Is your faucet or source of water opened completely? If you are trying to adjust flow or pressure using the faucet this is often the problem. Same if you are trying to adjust temperature with the faucet, COLD water only no hot or blending.

 

One issue with the small "portable" systems is they use smaller replacement filters which are not the same micron ranges reefers prefer and do not filter as well nor last as long. The sole purpose of a sediment filter is to protect the billions of tiny pores in the carbons surface and the carbon is to protect the RO membrane from chlorine so it does not melt. Chlorine does not register well as TDS and is at such low levels so I use a low rangle chlorine test kit (Spectrapure)to monitor for chlorine breakthru.

 

As already pointed out, you need to know the TDS of the RO only water before the DI since the RO is where 90-98% of the work is performed. The RO could be doing nothing and the DI is acting as a crutch to make up for it and may not last more than a few gallons before it is exhausted. You also need to keep that waste ratio around 4:1 so you have sufficient pressure for the membrane to work.

 

What is your water pressure at the membrane and what are your tap , RO only and final RO/DI TDS numbers? What is your exact measured waste ratio?

 

 

I will have to take the unit apart to test the water coming out after the RO but before the DI part. I've got family in town so I'll come back to it.

 

My waste to RO ratio is pretty close to 4:1, I measured it twice. First run was 18oz of waste for 4oz of RODI. Second run was 10oz waste and 2.5oz RODI.

 

My question wasn't so much about the TDS as the Chlorine, I just wanted to make sure that I didn't end up with Chlorine in the tank. My TDS is measuring zero but as you guys all mentioned that could mean the DI is being used up if the membrane is toast. At some point I will check it though because now I am curious.

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If the carbon is high quality and is less than 6 months old it should be able to remove normal residual chlorine amounts. Again though the portable systems use a smaller carbon and sediment cartridge than the normal units so the life will be less. A normal replacement carbon block, if it is protected by a high quality, low micron sediment filter will remove up to 20,000 gallons (16,000 waste gallons/4,000 treated gallons at 4:1 waste ratio)worth of chlorine at 1 mg/L residual for a 0.5 or 0.6 micron carbon block, 12,000 to 15,000 gallons (9,600 to 12,000 waste/2,400 to 3,000 treated gallons) for a 1 micron block, 5,000 gallons (4,000 waste/1,000 treated) for a 5 micron block and 3,000 gallons (2,400 waste and only 600 treated) for a 10 micron block and as little as 1,500 gallons (1,200 waste and only 300 treated gallons so almost worthless) for a granular activated carbon cartridge which many of the portable systems use.

 

These are all assuming you have an equal sized or smaller micron size sediment filter protecting the carbon and your Cl2 residual in your tap water is around 1 mg/L or PPM. If the system is using the carbon block as a sediment or particulate filter also then all bets are off since the crud is fouling the carbon and rendering it useless.

 

You can't really accurately see chlorine with a TDS meter, especially an inline meter which lacks the accuracy of a good ATC handheld.

 

At a minimum you want the three TDS readings, tap, RO and RO/DI which tells you a lot.

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