How to Build Your Own RO Filter

Written by naomi bolton Google
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How to Build Your Own RO Filter
Reverse osmosis will remove pollutants from tap water. (aquarium fish 5 image by cherie from

Inland marine aquarists frequently use synthetic sea salts in order to make marine water. The synthetic salt is mixed with tap water, which in its untreated state, often contains impurities, including nitrates and phosphates. Tap water for use in marine tanks must therefore be purified by passing it through a reverse osmosis unit. Reverse osmosis units normally contain prefilters, such as a micron filter to remove particulate matter and an activated charcoal cartridge to remove chlorine. The heart of a reverse osmosis unit, though, is the semi-permeable membrane that removes phosphates and nitrates.

Skill level:

Things you need

  • Reverse osmosis unit
  • Semi-permeable cartridge
  • Micron filter
  • Activated charcoal cartridge
  • Water supply, including garden tap
  • RO garden tap connector
  • 1 foot of connector pipe, 0.9 inch diameter)
  • 6-foot collection pipe, 0.9 inch diameter with in-line plastic tap
  • 30-foot exhaust pipe, 0.9 inch diameter with in-line plastic tap
  • 20-gallon plastic bucket
  • 2.72kg. of synthetic sea salt

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  1. 1

    Unscrew the top of the semi-permeable membrane cartridges and insert a membrane. Wet the tip of your finger and run it over the washer. Screw the top back tightly.

  2. 2

    Unscrew the micron filter cartridge and inset the filter. Wet the tip of your finger and run it over the washer. Screw the top back tightly.

  3. 3

    Unscrew the activated charcoal cartridge and insert the activated carbon filter. Wet the tip of your finger and run it over the washer. Screw the top back tightly.

  4. 4

    Screw the RO garden tap connector onto the tap and attach the 0.9-inch diameter reverse osmosis connector pipe to the tap connector.

  5. 5

    Connect the 30-foot exhaust pipe, 0.9-inch diameter, to the reverse osmosis exhaust site and run it into the garden or vegetable patch.

  6. 6

    Connect the 0.9-inch diameter collection pipe to the reverse unit and place the opposite end in a clean 20-gallon plastic bucket.

  7. 7

    Turn on the garden tap and ensure that the 0.9-inch diameter connector pipe is securely attached to the tap connector.

  8. 8

    Close the in-line plastic tap that leads to the bucket and open the in-line plastic exhaust tap. Turn on the garden tap fully and wait for 5 minutes while the reverse osmosis unit is flushed out, to remove any dust from the activated charcoal.

  9. 9

    Turn off the garden tap. Close the in-line plastic exhaust tap and open the in-line tap in the plastic bucket.

  10. 10

    Turn on the garden tap and allow the 20-gallon bucket to fill with pure reverse osmosis water. These units produce pure water at a slow rate, so depending on the garden tap pressure, it could take 3 or 4 hours for the 20-gallon bucket to fill.

  11. 11

    Turn off the garden tap once the 20-gallon bucket is full.

  12. 12

    Mix 2.72kg of artificial sea salt into the 20-gallon bucket and place a submersible pump and aquarium heater into the bucket to circulate and warm the water until you are ready to use it for your aquarium.

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