Backyard Aquaponics
A place to discuss aquaponics

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Just wondering if folk have experience with or know the answer to IF water that has been collected off a galvanised roof, can be filtered and used safely..

eg.. pumping through a carbon filter..???

I collect lots of water from galvanised roof surfaces and little from plastic.. It would be good to have the choice..
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I think the danger is from when the water is continually circulating through the pipes/galv. When it's only touching it once, it isn't a problem.

I've got the run off from my galv roof going straight into the pond, and it's caused no problems at all.

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As a not chemist, I would have totally agreed, but there is such firm opinion that Zn is bad..
Who am I to argue..

I had two thoughts - first, and like you, it is there in contact for sooo little time, but then, the roof has sat there prior to the rain and one is unsure of that first flush or rather how long it would take to consider safe B4 collecting..

Just trying to come to terms with past deaths where I am still unconvinced and the only certainty is that I used SOME water from the GAL roof when the "Plastic" water ran out..

ie either use filtered tap water of Roof Run Off..
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I had my rainwater tested that came from my zincalume roof and that had zinc levels in excess of those recommended for trout - never tried one to see if they were really a problem though.

its fine buidoi, after all my fish deaths i worked out that zinc was the culprit, so yes it is very bad, but only when in constant contact.

However constant contact can be pretty quick..... a 2.5kl tank can get back to 1.8ppm in less than a week easily.


my tests showed that water in a galv. tank will get to 1.8ppm (what mine got to max.) where as the water in my water tank, which all come from galv. roofs was still at 0ppm (or atleast below 0.6, which is the test minimum).

My test came to 0.15 ppm - that was just rain contact and storage in poly tank. My concern was that that level may accumulate when topping up using that water at 30% of system volume per week in summer.

it may.

i managed to get atleast a couple of trout to survive each year and grow to a very good size at 1.8ppm.
i did lose a lot of fish too though.

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Thanks for the obs..... greatly appreciated ..

So in summary, opinion suggests it is possibly OK to fill a system from water collected from a gal' roof' but held in a plastic tank, but, it would be wise to try topup from more pure water to reduce the effect of concentration over time..

Clearly, it is better to go for the best, but just what is that for the average punter..

What if you have no alternative... no plastic roof runoff..

SO....what would the preference be when the two options were runoff from the gal roof , and town water that has flouride and chlorine and? ???? Added...

And then the question of carbon filtering and what if any benefit, can come from their use..

Eg.. does a GOOD activated charcoal filter remove all. Or any contaminants from from town water and what effect would they have in helping??? With the likes of metals like Zn and Al and even Cu in rainwater..

Any informed opinions...

Peter..
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If you live in a city of millions, or even just downwind from a Copper smelter, the rainwater is going to be more acidic than it is in the country, which would lead to more Zinc being dissolved from a galvanised roof as the water ran from it. What pH is your rain water?

Also on ph, the toxicity to trout changes with alkalinity. From memory the higher the better - which is not great for an AP system where you typically want ph of 6.5

http://nepis.epa.gov/Exe/ZyNET.exe/9101 ... &File=D%3A\zyfiles\Index%20Data\76thru80\Txt\00000022\91013JZ5.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h|-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p|f&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL

Link doesn't work, but URLs like that need the TinyURL treatment, it's very handy for these ridiculously long URLS

yea link would need to be copy/pasted.... its not just the blue part, its the whole thing.

well seen as i cant edit it....... :rolleyes:

heres a better link copied straight from google -

nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=91013JZ5.TXT


also, can google "zinc trout" to find the document, its the first result for me, but ive viewed it a few times over the months.

Interesting question which I will have to consider down the track at the new property . I don't imagine that there would be much risk with rain runoff from a decade old galvanised roof into a plastic tank. However, continuous exposure of low pH AP water on galvanised fittings, pipes or tanks may be another matter, as could areas with acidic particulate pollution in the vicinity of heavy industry such as coal fired power stations. Gal corrugated iron roofing is all very rusty downwind of the Latrobe Valley.

It is specifically calcium, not alkalinity per se, that reduces accumulation of zinc in rainbow trout. Interesting paper on Calcium control of zinc uptake in rainbow trout http://mit.biology.au.dk/~biobaat/ecoto ... ticle1.pdf

Here's a summarised version of the abstract...
Water hardness is known to control the uptake and toxicity of zinc and other metals through either chemical competition, biological acclimation, or both processes. The dominant process controlling zinc uptake has not been previously elucidated, nor has the effect of calcium been investigated independently of other cations. Zinc uptake was approximately linear during the 24 h exposure period and uptake was calcium dependent. The results of this study demonstrate that calcium reduces zinc uptake through both biological acclimation and chemical processes, and that the protective effects of calcium are approximately additive.