If your RO product water is pure, your aquarium should have minimal algae growth, a steady PH level, and low phosphate and nitrate levels. You can check the purity of your RO product water using a conductivity meter, TDS meter, or by measuring the general hardness and alkalinity of the water with a test kit. Purified water will have a general hardness of 0 GH and alkalinity of 0 dKH. If your test values vary from those described above, you may need to replace cartridges and/or the RO membrane.
It's not likely that you received a defective unit. But there are a few factors that effect the output of reverse osmosis units. These factors include; the source water pressure, temperature, and the amount of total dissolved solids within the source water.
The ideal operating pressure for a RO (reverse osmosis) unit is 65 psi (pounds per square inch). An operating pressure of 45 psi will reduce the output of a unit by 50%. There are pressure gauges available to monitor the operating pressure of the system. If the operating pressure is too low, an RO pressure boosting pump can be added to increase the operating pressure to the ideal range.
The temperature of the source water should ideally be in the 70° to 77°F range for optimal performance. A temperature of 50°F, or lower, will reduce the output of the unit by 50% or more. Either hot or a mix of hot/cold tap water should never be used for the source water due to the minerals that are added to the water from most water heaters.
Finally, the amount of total dissolved solids in the source water can reduce the amount of water produced by a RO unit. If your source water contains a higher concentration, it would be wise to install a mechanical pre-filter in line prior to the unit. These filters are available at most hardware stores. Because of the requirements of reverse osmosis units, it is wise to purchase a unit that is rated above the gallons per day that your needs require.
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 (TDS 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 2-3 years. However, high concentrations of certain minerals such as calcium, iron, and magnesium will shorten the lifespan of the membrane.