RO excess water usage

[DongShenYin]

Can the water that's been filtered out of a RO unit be used for freshwater tanks? Or are the impurities so concentrated that it would kill the FW fish? How about mixing the excess water with tap water? Or how about using the excess water on hardwater species, like African Rift Lake cichlids?

 

[gobie]

I Hear A Lot Of Lfs Do This Exact Thing That You Ask About. The Thought Behind This Is As Follows. The Larger The Body Of Water The Fish Comes From The More Delecate. Thus Pond And Lake Fish Can With Stand Higher Concentrations Of Impurities And Be Less Stressful To The Fish. I Don't Know How True This Statement Really Is. This Came From My Biology Professer At Csu One Can Ony Assume The Guy Knows What He Was Talking About.

 

[Llarian]

The excess water has typically been filtered several times before hitting the RO membrane, so its probably ok. Usually that water has been through a sediment filter and a couple carbon filters.

That being said, my tap tests at ~45ppm RDS, the RO+DI output is 0-1ppm, and the waste water tests at around 130-140ppm, which never quite made sense to me given the pre-filtering.

If you really want to answer that question, take some waste water and have it tested to see what the remaining impurities are.

-Dylan

 

[DongShenYin]

Good idea, thanks. Maybe it's because the wastewater has such concentrated levels of impurities that it registers that high?

 

[Llarian]

I've only noticed it to be about 1:4 output to waste.

Assuming an input of 44ppm, if you strip all that out of one gallon in 5, you should end up with it being concentrated into 4 gallons:
44/5 = x/4
or ~55ppm

That's not taking into account the prefilters or the DI bed.

If anybody has an answer on this or can reproduce that behavior with their own RO+DI units, I'd be interested in hearing it.

-Dylan