My Experience with Galvanized Stock Tanks ...

[Swampgorilla]

It's not good.

I'm just posting this for the record. It's not conclusive because it's anecdotal and just based on my experience with them.

When my 133 gallon aquarium cracked - I moved my three goldfish into rubbermaid trash cans temporarily and then looked for another long-term solution. I started looking at the idea of using a galvanized oval-ended stock tank to make an indoor pond. There's plenty of people who've done it - you'll find all kinds of pictures if you google. There are others warn of zinc leeching into the water if you use these tanks - which wouldn't be good for the fish. But all of those who "warned" had never actually tried it.

So ... LOL, I tried it.

Bought a brand new galvanized stock tank and scrubbed the hell out of the inside of it with pure water. Put the fish in and they seemed fine. About five weeks later - the fish started acting lethargic even though the water parameters were perfect. The two biggest fish died - I got the two smaller ones out of the tank and moved them into the trash cans again. They survived and seem to be fine.

The only think I can attribute the kill-off to is the galvanized metal or some chemical on the surface that I couldn't remove.

It's been about four weeks now ... I sanded the inside of the galvanized tank - etched it with vinegar - applied self-etching primer and then painted the inside of the tank with Pond Armor Pond Shield. This stuff was fantastic to work with and the inside of the tank looks great.

The fish are now back in the galvanized tank with the Pond Shield epoxy liner - hopefully this will fix the problem.

Just wanted to post this so others can be cautious about using these tanks. I've personally seen others use them and there's plenty of folks on the 'net who use them and seem to have no problems. And although I can't scientifically trace my problem to the galvanized metal - I have no other explanation. The water was perfect and there were no parasites. Plenty of oxygen in the water and the symptoms of the fish prior to death were exactly what you'd expect with a slow-chemicallike poisoning.

EDIT: How come some people can use these tanks? I'm not sure - I've seen cattlemen with rusty old galvanized tanks outside in their fields with goldfish and minnows growing in them - with no filtration at all (though there is a steady stream of new water being introduced almost constantly to the tanks). The renewable water may be one reason. One reason may be that the tanks are old and all of the manufacturing chemicals are long since gone ... and the zinc leeching has stopped. Perhaps the reason I had a problem is my tank was new and full of brand new shiny zinc. And / or - perhaps these tanks are now made in China and they use some wicked chemicals in their galvanizing process. I don't know.

 

[Deadliestviper7]

I think if u plan on using these as fish tanks u should rinse with hose and leave on driveway for six months upside down. Stainless steel uses chromium I believe and this helps leach it out

 

[Pomatomus]

What is your water hardness? Zinc is more toxic when your hardness is low. Especially the calcium component.

 

[Pomatomus]

What is your water hardness? Zinc is more toxic when your hardness is low. Especially the calcium component.

 

[R Griftown]

I deal with a lot of corrosion issues in my line of engineering work. The Galvinizing on a steel tank is a "Sacrificial" coating. Meaning that the coating will actually disolve over time. To simplfy: The way galvonic corrosion works is the least noble element (In this caese the galvonic coating) electrically passes its Ions through the electrolyte (In this case the water) onto the more noble element (In this case the steel core of the tank.) Over time and depending on the amount of pin holes or abrasions reaching the steel, the galvonizing will come off pass through the water and deposit itself on the metal pin holes. My guess is that perhaps this process is putting the gavinizing into the water and thus into the fish. As the corrosion on the tank gets worse (More pinholes) the process speeds up. This is just an educated guess on my part. If you want to study galvonic corrosion, there is plenty of information online. As I said, I greatly simplified the explanation and an educated guess. I will stick to plastic stock tanks for safety.

 

[jjohnwm]

I've read many times about these tanks being dangerous to fish; I've never taken it too seriously because I used one for years when I was a kid as one of my first outdoor tanks and never had a problem. But others constantly claim they are toxic, and I admit that since hearing this I have never gone back to using one without coating the interior with some type of epoxy.

Now, here's the thing: if the zinc galvanizing is indeed dangerous due to releasing a slow supply of ions into the water...and if you never or rarely change the water...then of course this effect will be cumulative and will eventually harm your fish.

But, if your tank water is changed often enough and a sufficient volume is changed each time, you could probably build a tank out of cyanide and arsenic without having your fish suffer ill effects, since there will never be enough of a build-up to matter.

My outdoor galvanized stock tank was set up in the backyard of my family's home in rural Ontario, and a small pump kept a constant stream of water coming from a creek at the edge of our yard into the tank, with the constant overflow going into a small inground pond and then eventually down the hillside and into the woods. The tank held something like 150 gallons, and the pump was rated for over 800 gph. Assuming that it lost as much as 50% of its output to head pressure, friction, etc. and you are still talking a complete turnover of 100% of the tank volume 2 or 3 times every hour. That's a water change of about 35000% per week! Suddenly, your typical 50% weekly change sounds a bit anemic, huh?

Those ranchers with a constant flow-through in their tanks, with each cow drinking at least 10 gallons daily, might have less than that but it will still be a very thorough put-through on a continuous basis.

During the weeks leading up to the unfortunate demise of those fish, how many times was the entire water volume changed? Whatever it was, it likely didn't keep up with the introduction of whatever toxic substances were being introduced. In any case, a properly-applied coating of Pond Shield or some other aquarium-safe epoxy should keep your fish completely safe.

Edited to add: Dang. Seven-year-old thread. Gotta start watching out for that.

 

[dmyersWv]

I thought about trying the steel tubs, but have always went with the Rubbermaid or similar. Didn't want to chance the issues I've read about. Also the cost is very competitive.

 

[dmyersWv]

300 gallon Rubbermaid tubs have been great. Looking for some 125's to add to the fish room.

 

[tlindsey]

I deal with a lot of corrosion issues in my line of engineering work. The Galvinizing on a steel tank is a "Sacrificial" coating. Meaning that the coating will actually disolve over time. To simplfy: The way galvonic corrosion works is the least noble element (In this caese the galvonic coating) electrically passes its Ions through the electrolyte (In this case the water) onto the more noble element (In this case the steel core of the tank.) Over time and depending on the amount of pin holes or abrasions reaching the steel, the galvonizing will come off pass through the water and deposit itself on the metal pin holes. My guess is that perhaps this process is putting the gavinizing into the water and thus into the fish. As the corrosion on the tank gets worse (More pinholes) the process speeds up. This is just an educated guess on my part. If you want to study galvonic corrosion, there is plenty of information online. As I said, I greatly simplified the explanation and an educated guess. I will stick to plastic stock tanks for safety.

Welcome aboard
Thanks for sharing your knowledge on galvanized steel.

 

[jjohnwm]

I thought about trying the steel tubs, but have always went with the Rubbermaid or similar. Didn't want to chance the issues I've read about. Also the cost is very competitive.

Absolutely! If I were starting from scratch and had to buy the tanks new, a plastic tank would be the obvious choice. I would only consider a galvanized tank if I could buy it dirt cheap or get it free. I wasn't recommending them, just stating that they aren't completely off the table in all circumstances.

I just picked up an 8-foot diameter stock tank recently, on sale at a local farm supply place on an end-of-season clearance price that I couldn't pass up. Especially for the larger tanks, which take up a lot of space to store for the winter, now is a good time of year to find deals on stock tanks.