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RO Systems

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  • RO Systems

    I'm looking for a good RO System that is capable of puting out 100 gpd. My current setup will allowfor the mains water to pass through a large carbon filter and a standard water softener. I'm hoping with my prefiltration I can get away with just a basic unit.
    Does anyone here have any preferences or units that they have been using that they will recommend? Some of those units on ebay look very cheap and I am more than hesitant to purchase the cheapest unit available.
    Currently my plans are too let 100 gpd of RO water trickle into the pond and when doing maintenance switch over too just carbon filtered tap water which is very high in KH and GH. With a little tweaking I should be able to get the balance I am looking for.
    Any help or recommendations would be greatly appreciated.
    Thanks in advance,
  • #2

    I have a GE Merlin which does about 700gpd.
    It cost about $400. I got it on ebay, too.

    Solid unit.


    • #3

      When getting a reverse osmosis unit, check for the volume of waste created per gallon of RO water. A friend has expressed frustration with the amount of water being wasted. A person may need to think about uses for the waste water to make it practical in their situation.


      • #4

        They all waste a lot of water. So if you are willing to use one, don't be discouraged

        The more efficient the unit is at filtering out stuffs, the more water it will waste.

        After doing some research, I found the GE Merlin to be a good fit for pond. Gpd is good and doesn't filter out EVERYTHING (TDS is about 20)

        Good luck!


        • #5

          RO systems usually waste 2 gallons for every 1 gallon of good water. So it is a 2:1 ratio.


          • #6

            there are many good units out there that will do the job. With your water being prefiltered you'll be slower to replace cartridges and you'll have better return.
            I take my waste volumn and water my bonsai and garden plants with it. Kind of the mentality of those who put 55 gal barrels to gather rain from the gutters.
            Just be sure and check your mix so nothing changes. My unit has a TDS unit to measure before and after. I found it also on Ebay.
            Dick Benbow


            • #7

              Good stuff guys keep it coming as i am looking at getting an RO unit very soon.Dick i too will be keeping the waste to water my garden and plants as i am on a meter Gazza



              • #8

                hi guys

                i love ro thread, i think the merlin is a brilliant piece of kit for its money here its not quite as cheap as what you paid for it koiloco. Is 700 US dollars? For about 900 AUD i can get this unit, produces between 1500L at 50psi and 2500L at 100psi.

                this is a nice piecce of kit using 4 domestic membranes, flush valv, pressure gauges and in line tds monitor. its a 1 to 1 waste ratio.

                you can use the waste for washing the car or hookup a mid size submersible and water the garden, bathe the dog. Lots

                There is no such thing as a zero maintenance pond but the closer you get the more time to enjoy your koi. Soft low TDS water is the perfect pond water.


                • #9

                  Thanks for all of the input.

                  I have seen the merlin unit at ebay and it lists a "rejection rate of 90-99%". This is the part I don't understand. I find it hard to believe that 90-99% of the water is rejected as waste. That just can't be possible or else no one would use it. I'm on metered water and it is expensive. Does anyone have any clarification regarding how much goes to waste besides Tewa. I have seen so many differing quantities from many different boards.
                  As Dick says I'm also assuming prefiltration with carbon and a water softener will greatly decrease the amount of waste water produced?
                  Tewa, the unit you are using looks like it has more prefiltration than the standard merlin I can buy here in the states. I wonder if that accounts for the discrepencies regarding waste.


                  • #10

                    hey rob

                    The rejection rate you are talking about is what amount of solutes it rejects from water not the actual waste water ratio.

                    For eg if there is only 100ppm of salt in the water the merlin reckons it can take out between 90 to 99ppm.

                    i beleieve the merlin ration is 33% good water and 66% waste water. I think its wise to get a water report from your local water authority as, I heard that the merlin's prefilter gets blocked up via easily, when used here in western australia but we have rather dirty and bade water around 5 to 600ppm tds and there is plenty of sediment.

                    The dealer here easily hooked up other carbon filters that were more tolerant that the ones originally from GE.

                    The RO i posted has 2 sediment blocks followed by a carbon cartridge.

                    hope that helps

                    There is no such thing as a zero maintenance pond but the closer you get the more time to enjoy your koi. Soft low TDS water is the perfect pond water.


                    • #11


                      the waste water ratio depends on the individual unit. Those that are familiar with are using domestic membranes.

                      these membranes are hooked up in series to reduce the waste water ratio. It works by first having the tap water feed the prefilter then the first membrane the waste water from the first membrane then feeds the second and so on. Domestic units are usually 10 inch membranes and they have their limits as to the tds of the input water. For eg at 500ppm tap water the waste water from the last membrane comes out at around 1700ppm. Then there is the question of tap pressure, whether or not your tap pressure is strong enought to run a three or four membrane unit. Typically running on 1 membrane the water ratios are 1 part good water to 3 part waste water. For dometic units the best recovery you can get is 1 part good and 1 part bad water, you can probably push it to 60% good water to 40% waste water but this would shorten the life of the membrane.

                      If you use a strong booster pump you can recycle the waste water across another set of membranes (provided they can handle the tds of the final waste water from the 3rd membrane) but this booster must be able to handle the flow rate and provide the pressure these pumps are often expensive and run on 1hp to half horse power ie use alot of electricity if you have to run the ro 24/7.

                      The membranes on the merlin are semi industrial ie they are larger and the brilliant thing about them is they run without a booster pump.
                      There is no such thing as a zero maintenance pond but the closer you get the more time to enjoy your koi. Soft low TDS water is the perfect pond water.


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