BilgePump Posted June 12, 2014 Share Posted June 12, 2014 My home is on a well. Line pressure is usually ~45psi, and the unfiltered water has really high TDS (I think it was 600 last I checked). With the 45 psi going into my RO I am able to get the TDS down to 70-80. The problem, as I am sure you have guessed, is that I am burning through DI resin like mad. According to filmtec I should be getting 98% rejection, which would be more like 12 TDS. I had assumed for months that I was getting less than maximum performance from the membrane because it wasn't receiving enough pressure and went ahead and bought a booster pump (aquatec 8800). The pump arrived today and I got it installed and it pushed the pressure up to 90psi. After flushing some water through I turned on the meter and watched the TDS start to drop down into the 70's and 60's, and then inexplicably begin to rise. It kept rising up to the 102 mark, before I shut the meter off and began to scratch my head. Could the increase in pressure be flushing stuff out of the filters perhaps? Any suggestions would be appreciated. Also, I'm getting air bubbles now, which cant be good for the RO and is possibly also related to the TDS increase. What I really need to be doing is a water change on my tank. Link to comment
BilgePump Posted June 12, 2014 Author Share Posted June 12, 2014 After flushing some more water through the line my TDs is down in the teens! I think my hypothesis about the pressure increase flushing out the filters might have been correct. My DI resin should last ages now! Link to comment
jedimasterben Posted June 12, 2014 Share Posted June 12, 2014 If your TDS is still in the teens before your DI resin, you will absolutely want a booster pump. Even with that being much lower than before, you're going to burn through a very large amount of DI resin, and it will be MUCH cheaper to purchase a booster pump. Link to comment
AZDesertRat Posted June 13, 2014 Share Posted June 13, 2014 What is your exact measured waste ratio? You may not be sending enough to waste causing the membrane to foul and plug. With tap TDS that high you should be at a minimum 4:1 waste ratio. Also do you have a water softener? Membranes love soft water. The other big thing I suggest is a good handheld TDS meter, inlines lack accuracy mostly due to not being truly temperature compensated plus they are dedicated to two spots while you need 3 TDS readings with a RO/DI. I have two dual inlines gathering dust, I only trust my handhelds. Link to comment
BilgePump Posted June 13, 2014 Author Share Posted June 13, 2014 I am presently using a booster pump. What is your TDS reading pre-DI jedimasterben? With the booster installed I am getting the 98% advertised rejection rate out of my filmtec membrane. I suppose I could add another sediment filter or look at a dual membrane system, but for the moment 12 TDS (pre-DI) will have to do... Link to comment
BilgePump Posted June 13, 2014 Author Share Posted June 13, 2014 What is your exact measured waste ratio? You may not be sending enough to waste causing the membrane to foul and plug. With tap TDS that high you should be at a minimum 4:1 waste ratio. Also do you have a water softener? Membranes love soft water. The other big thing I suggest is a good handheld TDS meter, inlines lack accuracy mostly due to not being truly temperature compensated plus they are dedicated to two spots while you need 3 TDS readings with a RO/DI. I have two dual inlines gathering dust, I only trust my handhelds. I haven't measured my waste ratio. Do I just put the waste water line in a bucket or something and use the RO system and then compare results? I do have a water softener as well. Thanks for the advice about the handheld meter, I only have one of the dual inline versions (measuring the RO and DI outputs). Link to comment
AZDesertRat Posted June 13, 2014 Share Posted June 13, 2014 Sediment filters don't remove TDS, they trap big stuff. TDS is in the 0.0001 micron range, a sediment filter is usually in the 10, 5 or 1 micron range, thousands of times too coarse to remove TDS. Dual membranes also don't remove more TDS or save water, they are used to give you more water faster. To measure the waste ratio you need a measuring cup and a clock or watch. Measure the waste flow for exactly one minute the write the amount down in either ounces or milliliters then do the same with the treated flow for exactly one minute. What are the two amounts and is the waste about 4 times as much as the treated? Are you using softened water for the RO/DI? If not you should be. Link to comment
BilgePump Posted June 13, 2014 Author Share Posted June 13, 2014 So based on the fact that I am using soft water, a booster pump and that my membrane is giving the advertised performance (98% reduction), it is probably safe to say that I'm not going to get the TDS any lower. How many TDS do most reefers get out of their RO systems? Link to comment
jedimasterben Posted June 13, 2014 Share Posted June 13, 2014 I am presently using a booster pump. What is your TDS reading pre-DI jedimasterben? Pre-membrane is 312 and post-membrane is 2. 99.36% rejection rate. Link to comment
AZDesertRat Posted June 13, 2014 Share Posted June 13, 2014 You could invest $50 or so in a Spectrapure Select high rejection rate hand tested membrane guaranteed to be 99% or better. My tap TDS is 560-800+, I do use a water softener and my RO only TDS is between 2 and 3 always. The membrane will be 7 years old in a couple months and it has more than paid for itself in DI savings. When I was using a off the shelf Dow Filmtec my RO only TDS was between 13 and 15 and I even replaced the membrane and has it bench tested. The difference between 98% and 99.4% in my case is a huge savings. Link to comment
BilgePump Posted June 13, 2014 Author Share Posted June 13, 2014 I think I will look into the spectrapure membrane... Thanks for the help guys. Link to comment
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