Can I Use Reverse Osmosis Filter Waste Water -- that's been through a water softener?

[Dan Knauss]

I live in NW Iowa where the water is really hard at 38-40gpg. The pH is 7.5 and TDS is 500ppm mainly from calcium. (CH=800+ppm, KH=250+ppm.) The city water also comes with 5-10ppm Nitrates and 30-40ppm Sodium. 

Am I right this is not really ideal water for fish or plants? :)

After going through a water softener with salt (NaCl) but using the absolute minimum, pH is the same (7.5), TDS goes up to 675, CH falls to under 100ppm, and KH is a little less at ~200.

I know sodium salt softened water is really not supposed to be good for fish or plants, but our house plants seem to do OK with it. 

We also have an old 3-stage basic RO filter that produces an enormous volume of wastewater, so I have been capturing the waste in an IBC tote I was hoping to use for aquaponics. The RO brine has the following profile:

TDS=600

pH=7.5

KH=215-240

CH=0-100

GH=100-125

I had a friend keep 3 big channel cats in the tote (200 gallons of RO waste water) for 2 days before they started to use up the dissolved oxygen and started gulping at the surface. (So we ate them.) There was no aeration system, unless you count the drip of the RO waste line feeding in, so I would like to think they could survive in this water with sufficient oxygen. Am I nuts? Pool salinity test strips don't seem reliable enough to count on, but they indicate the RO brine is around 100ppm salt. 

Even if I can keep brackish water fish in these conditions, what about plants? Does anyone do aquaponics based on a sea/rivermouth ecosystem? Could I improve the RO wastewater quality with a simple charcoal filter?

My original goal was to do something useful with all the water we are wasting from the RO system, but I can probably increase its efficiency a lot with a permeate pump -- something I recently learned. I'd still be interested in using this flow of RO waste somehow, but maybe that is pointless. Should I just use unsoftened tap water?

[Michael & Kristine Stoddard]

I wish someone would reply. I have a very similar idea and would love to know the answer.
Good luck. Hope you can figure something out.

[Alex Veidel]

If this helps at all, I would recommend bypassing the softener and buying some muriatic acid to bring your pH and carbonate hardness down. It pretty strong and dirt cheap (think $5 per gallon). My well water runs at 8.5 with a dKH of 18 (ppm of around 320 I believe) and it only takes 8 Tbsp of muriatic acid to bring 55 gallons down to a pH of around 6.5.

Muriatic acid is a little strong to add straight into the aquaponic system, so I recommend getting a 55 gallon barrel to do your initial treatment. I've been using an airpump (2.0 cu. ft. per minute) to mix and aerate the water before putting it into the system.

[Jim Fisk]

Anyone tried hauling water from a local healthy stream or lake? A 330g IBC and 12v pump in a PU truck might be the easiest answer. Find a source where fish are thriving naturally. Even the fire dept might help with a larger system with a donation. I feel your pain and picked a part of the country where this is not a problem when we retired. Poor water really sucks in so many ways.