Originally Posted by mike31154
I have no experience with freshwater aquariums, but I would surmise that the benefits of using RO water are the same for both salt & freshwater systems. With RO you are starting with a "known" water quality, that is, there are no "unknown" impurities or dissolved solids in the water you are about to use.
Most likely you can use the waste water from your RO system for your freshwater tank no problem, after all, it does originate from a source that's safe for human consumption. But without a city water report that shows what's in your tap water, you really have no idea what you're adding, in what concentration and/or what you need to dose to correct the levels of whatever you consider desirable for your freshwater tank. Keep in mind that the RO waste water is a more concentrated soup of whatever comes out of your tap, with some sediment & the chlorine removed. Even with a city water report, the report is only a snapshot & water quality can vary considerably depending on the season & what the city uses as a source. You'd need a pretty comprehensive kit or home laboratory to test for all those minerals & impurities yourself.
Below are two water reports from my provider, the City of Vernon. We have multiple water sources & there are occasions when they switch supplies to various customers due to spring run off, turbidity, water quality issues etc. Reports show Kalamalka Lake source which supplies most of the water & the Duteau Creek source which they recently spent millions on to improve quality. Duteau Creek is much softer water. 99% of the time, I am on the Kal Lake source & my TDS reading out of the tap these days is fairly consistent between 165-170.
North Kalamalka Lake Intake Water Quality 2008
Water System: Greater Vernon Water
Source: Kalamalka Lake
Facility: Kal Lake Pumpstation
Sampling Point: Kal Lake Intake
Date: 7/14/2008
INORGANIC Results (mg/L unless noted)
Aluminum <0.050
Antimony <0.0030
Arsenic <0.0050
Barium 0.027
Boron 0.021
Cadmium <0.00010
Calcium 40.6
Chloride 5.38
Chromium <0.015
Copper <0.0030
Cyanide < 0.01
Fluoride 0.24
Iron <0.20
Lead <0.001
Magnesium 19.8
Manganese <0.0050
Mercury <0.00030
Molybdenum 0.005
Nitrate (as N) 0.069
Nitrite (as N) <0.010
Potassium 5.07
Selenium <0.0050
Sodium 18.4
Sulphate 51
Uranium 0.003
Zinc 0.011
PHYSICAL Results (mg/L unless noted)
Alkalinity (as CaCO3) 152
Colour <5 TCU
Conductivity 409 microS/cm
Hardness (as CaCO3) 183
pH 7.8
Total dissolved solids 238
Turbidity 1.0 NTU
Water System:Greater Vernon Water,
Source: Duteau Creek
Facility:Headgates
Sampling Point:Headgates Cl2 bldg (1-1-SR, 5E8D)
Date of Sample:7/19/2011
INORGANIC, Results (mg/L unless noted)
Aluminum (total) 0.114
Antimony (total) <0.0010
Arsenic (total) <0.0050
Barium (total) <0.050
Boron (total) <0.040
Cadmium (total) <0.00010
Calcium (total) <5.0
Chloride 0.21
Chromium (total) <0.0050
Copper (total) 0.0245
Cyanide (total) <0.01
Fluoride 0.13
Iron (total) 0.31
Lead (total) <0.0010
Magnesium (total) 1.23
Manganese (total) 0.02
Mercury (total) <0.00020
Molybdenum (total) <0.0010
Nitrate (as N) 0.02
Nitrite (as N) <0.01
Potassium (total) 0.8
Selenium (total) <0.0050
Sodium (total) 1.36
Sulphate 3.1
Uranium (total) <0.00020
Zinc (total) <0.040
PHYSICAL, Results (mg/L unless noted)
Alkalinity (Total, as CaCO3) 14.3
Colour 75
Conductivity 38 microS/cm
Hardness (total, as CaCO3) <12.9
pH 7.14
Total dissolved solids/TDS 44
Turbidity 0.9
There are plenty of other uses for RO system waste water. Some folks use it to fill their washing machine, but to me that's pretty hard water & I'd rather not have that stuff filtering through my textiles. I use it in the garden & to flush toilets. Been considering a 'grey' water system in my house to lower the water bills. I could plumb the RO waste into that. The way things are going with rate hikes around here, if I don't do something, I may even need to give up the hobby, along with my garden.
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