Reverse Osmosis: Checking Aquarium Water Purity
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Q. Is there any way I can check the purity of the water my reverse osmosis system is producing? Also, how often do I have to change the membrane?
 
A. Reverse osmosis (RO) systems remove most of the impurities (heavy metals, minerals, nitrates, phosphates, and so on) in tap water, giving you pure, healthy water for your aquarium. If your RO product water is pure, your aquarium should have minimal algae growth, a steady pH level, and low phosphate and nitrate levels. If these conditions change, check your RO product water purity using one of the following methods:
  • Use a conductivity meter, which will accurately measure the amount of impurities in the RO product water. Whereas regular tap water will have a reading in the range of 300-500, purified water should be in the range of 5-25.

  • Measure the general hardness, alkalinity, and pH of the water with a test kit. Purified water will have a general hardness of 0 GH, alkalinity of 0 dKH, and a pH of 7.0. If your test values vary from those described above, you may need to replace the membrane.

The lifespan of the RO membrane depends upon the quality of your source water. Under most conditions, an RO membrane will produce about 25,000 gallons of purified water and last 3-5 years. However, high concentrations of certain minerals such as calcium, iron, and magnesium will shorten the lifespan of the membrane. Consider installing a reverse osmosis flush kit, and use it weekly to flush out excess minerals. This should extend the lifespan of your RO membrane.

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