Thanks for your reply
Amedean Messan wrote:If water is so valuable that you are willing to forgo on the soap then sure. The nutrient obtained would be almost negligible and not worth the effort I suspect.
I plan to make my own soap. Just lye from wood ash and some lard. I am under the (possibly false) impression that this wont hurt the fish and it will repel certain pests in the garden. I will be in SoCal where it is hot year round, and according to worldweather.com, in the wettest month (feb) receives only 3.13 inches rainfall average and the driest (july) .07. That would make the water very valuable indeed because irrigating the garden any other way would be too expensive.
From what i understand, water from fish tanks has levels of nutrients that are well above "negligible". What leads you to suspect that they would be in this case?
I imagine this doing everything that a regular, closed look system aquaponics setup would do just without any electricity. The water splashing into the sinks and bathtubs and then being poured into the grow tank would aereate it and then the constant inflow of new water would prevent nitrates from becoming too concentrated (in theory). The nutrient rich water (up for debate) then goes into the garden and both irrigate and fertilizes. All of this occurs without any extra electricity from the pump. This would also eliminate a lot of the up-front labor to set up a system since the only thing one would have to do is to build/ obtain a grow out tank, put it under the grey water output and install an elbow pipe for overflow that is directed into the garden.
That being said, none of that matters if simple soap is harmful to fish.