ps2cho Posted August 24, 2015 Share Posted August 24, 2015 So I am currently burning through one maxcap di every 4 to 6 months. My current spectrapure 90gpd membrane is giving me 97.9% 10ppm out of 460ppm. Is it worth getting a spectrapurr 99% membrane to replace mine OR buying a piggyback 2nd RO membrane? What do you guys think? Link to comment
seabass Posted August 25, 2015 Share Posted August 25, 2015 Piggybacking another RO membrane won't improve water quality (it would increase production, but requires at least 65lbs of water pressure). You would be better off with with a more efficient RO membrane. This will reduce TDS to the DI stages and increase their useful life. Link to comment
AZDesertRat Posted August 25, 2015 Share Posted August 25, 2015 seabass nailed it. Dual membranes actually slightly decrease wate rquality since you are sending the concentrated waste or brine from the first membrane into the second membrane so the TDS usually goes up slightly due to the higher inlet TDS. With efficient membranes its not a deal breaker though for most but a RO booster pump also increases GPD but water quality goes up since membranes work better at higher pressure. The other thing is many vendors mistakenly promote dual membranes as a water saver and this is not true. Since you are sending the brine from the first into the second it is even more critical you keep the waste ratio up or you run the risk of premature membrane failure due to plugging and fouling. I am using the 99% membrane with a booster pump set at 95-100 psi here in Phoenix with a tap TDS averaging 530 to 560 right now and the RO only TDS is between 2 and 3 for a 99.43% average rejection rate. MaxCaps last a year and SilicaBusters last 3 years. If you can increase the rejection rate from 97.9% to 99% you should increase your DI life by about 50%. Another option I would suggest looking at is keeping your existing membrane and adding an Aquatec 8800 booster pump. You will increase the rejection rate to the same 99% or better and also increase the 90 GPD to between 125 and 150 GPD depending on the pressure setting. If you are wanting both better rejection rate and more water this is the better option. Link to comment
AZDesertRat Posted August 25, 2015 Share Posted August 25, 2015 Another thing I forgot to mention is using softened water. All membrane manfacturers recommend softened water and many will not honor a warranty claim if soft water was not used. Notice on the Dow Filmtec and other membrane sites their test results say 77 degrees F, 50 psi and 250 TDS softened water were used for the testing. Membranes love softened water since it does much of the work for them ahead of time. When I made the switch from our Phoenix hard water to a Sears water softener my rejection rate improved but the real difference was in component life like valves, faucets and water heaters. Link to comment
Admonition Posted August 25, 2015 Share Posted August 25, 2015 I am using the 99% membrane with a booster pump set at 95-100 psi here in Phoenix with a tap TDS averaging 530 to 560 right now and the RO only TDS is between 2 and 3 for a 99.43% average rejection rate. MaxCaps last a year and SilicaBusters last 3 years. Are you using that Aquatec pump you mentioned? I'm debating the same situation as the OP and it sounds like your suggestion of a booster pump is a better option than purchasing that piggyback item. Especially since I have the same parameters as you (minus the pump) and my PSI is 60 from the faucet. Link to comment
AZDesertRat Posted August 25, 2015 Share Posted August 25, 2015 Yes, I have the Aquatec 8800 with the pressure switch. My tap pressure is 65-68 and the extra 30 psi boost makes a big difference. If you really want to get technical and calculate your RO membranes actual performance you can use this worksheet found on the Spectrapure website. http://spectrapure.com/manuals/CALC-FORMULA.pdf Plug in different numbers and you can see how tap TDS, pressure and temperature affect membrane efficiency. Its a good thing to do maybe once a year to see how well your system is performing. Link to comment
Admonition Posted August 25, 2015 Share Posted August 25, 2015 Awesome thank you. Is this it? http://www.bulkreefsupply.com/1-4-aquatec-8800-booster-pump-kit.html It's says it comes with that pressure switch you mentioned, along with some other stuff? Link to comment
ps2cho Posted August 25, 2015 Author Share Posted August 25, 2015 So how does it work if I have one membrane at 99% and the other at 97.9%? Link to comment
seabass Posted August 25, 2015 Share Posted August 25, 2015 So how does it work if I have one membrane at 99% and the other at 97.9%? The first membrane will filter 99% of the impurities out of the water. These impurities (the waste water) will be sent to the second membrane (at a TDS higher than the original tap water) where it will filter 97.9% of the impurities out. The product water from the two membranes is then sent to the DI cartridge. You could switch the order of the membranes if you want. - http://spectrapure.com/huds/DUAL.pdf Link to comment
AZDesertRat Posted August 25, 2015 Share Posted August 25, 2015 http://www.reefcentral.com/forums/showthread.php?t=2342795 The combined rejection rate would be 99+97.9/2 or 98.45% theoretically. As they mention in the above link, I would use a booster pump instead of dual membranes. I used to own a MaxCap dual membrane system, it was my second MaxCap after a 90 GPD system but has been replaced by the MaxCap UHE-100 about 7 years ago. The dual membrane was a good system but I wanted even better water quality and longer DI life and get that with a single membrane and the booster pump along with 150+/- GPD. Link to comment
ps2cho Posted August 25, 2015 Author Share Posted August 25, 2015 My house supplies me 60psi water so sounds like the booster pump is the best choice Link to comment
AZDesertRat Posted August 25, 2015 Share Posted August 25, 2015 60 is pretty good but use the worksheet I attached in post #6 of this thread and run the numbers with different pressures to see what 70, 80, 90 and 100 would do for you. My first choice would be a water softener if you don't already have soft water and you own your home. Second would be the booster and third would be a new 99% membrane. For those who may be interested in the MaxCap UHE-100 ultra low waste systems, I saw Spectrapure has 10 of them on sale first come first serve over on Reef Central for $749. Thats $200 off of the everyday price and $150 off of the usual sale price of $899. Link to comment
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