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Run the system for awhile, it should come down further as the membrane becomes "seasoned". Try to make large batches of water when you do run it versus smaller batches where the membrane does not really have a chance to flush itself.
What is your water temperature and your exact measured waste ratio now? Are you using softened water or do you know your calcium carbonate hardness?
At 50 psi your rejection rate is low you will need at least 600 si to get a 98% rate. Is the pressure reading you are getting before or after membrane. What is it going into the second membrane.
The dual membrane systems you see all send the waste from the first membrane into the second membrane to increase the GPD, not to save water or further treat the water.
What you describe would require a booster pump since the water exiting the first membrane would be basically at atmospheric pressure and would have to be repressurized to get it through the second.
Do not believe the water saving some vendors claim, dual membranes are not water savers and will fail prematurely if not kept well flushed, this has been demonstarted many times by vendors with much more experience. Note none of the long time vendors, those with say 15+ years in the industry make this claim, they all know better. When you send the concentrated brine from one membrane into a second membrane it is even more important to keep the waste ratio up or both membranes suffer a shortened life driving the cost of ownership up. Dual membranes are to increase production, not to reduce waste.
Membranes are not all the same and some are much better than others. My tap water TDS varies between 550 and 850 and my RO only TDS varies between 2 and 3 always with DI lasting over 1000 gallons per cartridge. You can buy a hand tested 90 GPD RO membrane guaranteed to be 99% rejection rate for only $55 here:
NEW 99 Percent Rejection SpectraSelect Plus? 90-GPD RO Membrane
Here is an article documenting what that 99% means to you:
FAQ p.2
A few questions, what is your tap water TDS? Do you know your water hardness or do you have a water softener? What is your water pressure and water temperature? What is your exact measured waste ratio? Do you have CO2 in your water or if you don't know try using this nomograph to measure it, CO2 eats DI regardless of the T
The following link is a test run by Bulk Reef SupplyThe dual membrane systems you see all send the waste from the first membrane into the second membrane to increase the GPD, not to save water or further treat the water.
What you describe would require a booster pump since the water exiting the first membrane would be basically at atmospheric pressure and would have to be repressurized to get it through the second.
Do not believe the water saving some vendors claim, dual membranes are not water savers and will fail prematurely if not kept well flushed, this has been demonstarted many times by vendors with much more experience. Note none of the long time vendors, those with say 15+ years in the industry make this claim, they all know better. When you send the concentrated brine from one membrane into a second membrane it is even more important to keep the waste ratio up or both membranes suffer a shortened life driving the cost of ownership up. Dual membranes are to increase production, not to reduce waste.
Membranes are not all the same and some are much better than others. My tap water TDS varies between 550 and 850 and my RO only TDS varies between 2 and 3 always with DI lasting over 1000 gallons per cartridge. You can buy a hand tested 90 GPD RO membrane guaranteed to be 99% rejection rate for only $55 here:
NEW 99 Percent Rejection SpectraSelect Plus? 90-GPD RO Membrane
Here is an article documenting what that 99% means to you:
FAQ p.2
A few questions, what is your tap water TDS? Do you know your water hardness or do you have a water softener? What is your water pressure and water temperature? What is your exact measured waste ratio? Do you have CO2 in your water or if you don't know try using this nomograph to measure it, CO2 eats DI regardless of the TDS.
FAQ