Backyard Aquaponics
A place to discuss aquaponics

Given that the referenced document found LC50 concentrations as low as 0.1 and 0.24 from different studies, I would have to start to suggest that almost ANY Zn is potentially lethal for trout..
My understanding of LC50 is that 50% will die at that concentration..

which suggests that the "Test" is completely useless

So, the suggestion is that water from a Gal-Roof can come in at 0.15 and tested LC50 of 0.1 is reported..

Seems pretty conclusive.. NO GAL-ROOF WATER

the remaining part of the question is
SALVAGE.. is there any filtering that can remove Zn AND other toxic metals..

and another point - has anyone seen analysis of typical Sydney Tap Water..

clearly, I am trying to work out the safest form of water supply when "PURE" (??? ) rainwater is unavailable..
Many APer's that I have encountered just use tap water..

Thanks for the rational discussion and comments..
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the amount of zinc depends on acidity of water, age of metal, length of time on metal, etc.
i wouldnt say that its conclusive at all.....


http://nepis.epa.gov/Exe/tiff2png.cgi/9 ... 013JZ8.TIF


nor was the test useless..... its not an aquarium zinc test.... find me an aquarium test for zinc if you think its so useless...

I tend to agree, but when you take into account the WORST CASE conditions, it does have to be questioned if standard measurement capabilities can even safely predict the results of ANY Zn..
Increase the pH and increase the calcium carbonate and you MAY mitigate the effects, but to certain and not wonder why SOME died or any, it would nice to just eliminate Zn from the scene..

So again I go back to my FIRST question... Is there a know and reliable method of removing such contaminants.. ie.. DOES a carbon filter actually work or is there ANY filter or chelation method that can be used..
The deafening silence makes me think that there is NO WAY or no one knows of a way, or ever tried a way of removing toxic metals, and even large (semi-industrial) "CARBON" filters do nothing..

We see the docos about well water contamination from fracking in the USofA and wonder how these folk could ever venture into AP, with anything but the toughest of fish species, but then... how could you EAT a fish that has lived in such contaminated water..

KOI have survived my water, but natives seem to have read the LC50 stories and the 96hr experiments

Perhaps I should have been more specific and headed the thread with something like
" Reliable Pre-Treatment of suspect AP water "
..
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ive searched for a while and have found no reliable method.

i bought cuprisorb because i read it takes out "heavy metals", but it didnt seem to make a dent in my zinc levels.

i never tried carbon, i think i read it may work, but there isnt much info out there.

also heard zeolite may work, but havent tried that either, simply because of laziness and cost of trying all these things.

..
and thanks for the obs'..
out of curiosity how did you measure your Zn levels.. Professional analysis or a test kit..
Just wondering if test kits have an accuracy that matters .. ie.. by the time you get a true positive number, it may (according to that paper) be too late anyway..

fish can be such touchy creatures.. a bunch of KOI sharing the same water as Silver perch survive for many weeks and the perch (of the same size) are dead within 96 hrs, and the Nitro readings are all zero..
Grrrrrrr and RRR
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yea species matters more than anything else basically, i never had a single goldfish death from the zinc, although ive always gotten some fish from the other species i tried to live, 99% usually ended up dead - trout, SP, bass, murray cod, catfish, i havent had catfish deaths either, although the tanks are gone and water changes have been done since.
zinc is now low enough for some baby cod to live..... but it is still there, must have adsorbed into the rocks or fish waste, etc. TBH, last time i tested it was even higher than when the tanks were in use or some reason.

i bought a hanna instruments test kit, i cant link to it, i think they changed them since. that was the lowest increment test they had in stock, they have lower ones now though.

Hanna Instruments still have a Zinc test kit listed< http://www.hannainst.com.au/learn_more/i:HI+38076 >, supposedly it will measure down to 0.1mg/l, but it's no longer available, and hasn't been replaced with anything else.

yea they seem to be all over the place with thier zinc tests, when i bought they listed a 0.3, but only had 0.6 in stock, after buying the 0.6 they stocked the 0.1.... now you are saying they dont have that anymore.

however, they are the only company that i have found that you can get the needed tests outside of simple little aquarium tests.

Yea, they definitely don't have them any more, I spoke to the sales rep today. I want one, just to see what my Zn concentration is like, as some water in both systems has come from a 22500l galvanised tank... but it it probably fine as I've had zero deaths from over 300 trout and salmon so far (other than a few jumpers early on when I had no cover in place)

And I am starting to wonder if that is my problem.. I would occasionally use the Zinc-Roof water as top up, and then, after the electrification kill off, nothing was right again..
I am now thinking that you may have hit the nail on the head.. The problem built up and is slow to abate..

I am now nervous that the transplanted clay, from the old system to the new one (for bacteria) may carry the same disaster with the bacteria..
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.peter