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I'm told leaching zinc from my galvanized stock tank fish tank will not be good for the fish.  So, I'm going to either paint the inside of the tank or put a plastic membrane of the kind used for backyard landscape pools in it as a liner.

 

I'm wondering what paints will be safe for fish - fish I intend to eat. I'm wondering the same about the plastic membrane, although those are supposed to be (the packaging says so) safe for fish.

 

Anybody have any ideas?

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howdy Hal..

i've seen quite a few "pond paints" like pondarmour.. just double check to make sure it's safe for potable water..big bucks!

from what little investigating i've done, it looks like an epdm liner is a bit cheaper and easier

Hi there Hal. Zinc will absolutely leach and eventually kill your fish. Painting galvanized steel and getting it to last for more than a few years is kinda a pain in the ass.

Firstly, most galv steel is coated with a very thin layer of oil which prevents "white rust"...it's just part of the galv process, weather hot-dipped or batch processed. This outer layer makes it quite difficult for paints to stick well over even a relatively short period of time (like a year or two). Secondly, depending on the paint you use, the zinc itself may react with the paints binder(s), again resulting in chunks flaking and peeling off after a relatively short time.

First you want to use an alkaline base with a pH no greater than 11 or 12. Ammonia diluted to the right strength works just fine. Then you want to rough up the surface you want to paint. If you have access to a sweep blaster you can use a number of materials (like walnut shells, limestone, corn cob, or sands that have a Mhos hardness of 5 or less). If not then just use some really fine grit sand paper and be real careful not to take off to much of the galv layer.

After that you have a few options for preparations prior to painting...You can use a two part epoxy sealer (top coat over penetrating sealer), or a zinc phosphate treatment (spray and wash off after 3-5 minutes). Wash primers, or an acidic acrylic passivization technique probably isn't recommendable since they are easy to fuck up leaving you with too thick a protective layer (resulting in once again, flaking peeling paint). Anything over 12-13 microns for a wash primer is iffy, even less for the AA technique, over 1 micron and you're screwed...

Then you can primer and paint away...I don't know if you've ever painted galvanized gutters or anything before, but proper preparation before painting is paramount (hehe try saying that 5 times fast)...I also had a chance to see how some of this is done an an industrial/professional level, when I got called to do some non-destructive testing at a facility that produces galvanized sheet metal as well as at some of their off-shoot companies that produce a variety of products from that sheet metal...some of it painted. Believe me, you cant just slap some paint on there and expect it to stick. My gutters are holding up real well after six years. Ammonia wash, light sanding then primer then paint. As to whether they are fish safe gutters IDK...Not sure exactly how long they'll keep up lasting either.

Careful with liners too, landscaping stuff isn't necessarily made to be used in a re-circulating food production system containing aquatic life. If you've taken the trouble to set up a system, go the extra mile to make sure it's safe for the fish, the bacteria and for your family. Some longstanding Aquanut's here have used Firestone's fish safe EDPM liner. The vigin LDPE liner from Duraskrim I used for my rafts isn't really flexible so is not conducive to shaping...Good luck :)

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