Aluminum Water Tank Corrosion ?

[St. Elsewhere]

My potable water system consists of a welded aluminum water tank in the bottom of the hull with a suction line that runs through a strainer to a pump, and then through filters and on to the various locations of use. Early on, like 12 years ago, I was quite concerned to find an accumulation of white granular material in the bottom of the strainer. I did some investigation and found that the tank was not connected to the bonding system, so I added such connection, but the white granular material continued to appear. I had the material tested and it is indeed aluminum oxide.

In the years since the issue has continued to appear, but at a reduced rate. I have been concerned that it would result in a hole in the tank, but it has not done so yet. I am wondering if it is coming from loose bits of aluminum in the tank from the original welding process, or if it is indeed the walls of the tank disappearing.

Does anyone have any ideas?

[Hud3]

I had those crystals in my aluminum tank. They would clog the pump screen and the aerators on the faucets. I solved the problem by never letting a drop of chlorinated water into the tank again. No more crystals!

If you fill from a chlorinated public water supply, run the water through a carbon filter. You can buy the parts and put it together yourself. The filters are the canister type used for whole-house filters and RVs. Lowes and Home Depot sell them in the U.S.

[Fuss]

Originally Posted by Hud3

I had those crystals in my aluminum tank. They would clog the pump screen and the aerators on the faucets. I solved the problem by never letting a drop of chlorinated water into the tank again. No more crystals!

If you fill from a chlorinated public water supply, run the water through a carbon filter. You can buy the parts and put it together yourself. The filters are the canister type used for whole-house filters and RVs. Lowes and Home Depot sell them in the U.S.

Are you sure about that Hud?
How long ago did you start using the filter?
For how many gallons/liters does 1 filter last?

The reason i ask is that i also have this problem and if what you say is right then i am getting a carbon filter immediately.
John

[GordMay]

Carbon filtres are most effective at removing CHLORINE, sediment, and volatile organic compounds from water.

[Hud3]

John,

I had crystal problems for the first couple of years that I owned the boat. It was a damn nuisance, 'cause the pump screen would clog every few weeks, usually at a most inconvenient time, and I'd have to go down under the setee and clear it out. Mumbling and cursing, of course.

I ended up doing three things. I kept chlorine out of the tank by using well water, or by running municipal water through a charcoal filter. I also installed a second, coarse particle filter in the discharge line from the pressure pump, mounted near the pump. That kept any residual crud from getting into the aerators, and also allowed me to do the third thing, which was to use the filter housing (without the filter), as a receptacle into which I poured a half cup of Chlorox into in order to sanitize the freshwater plumbing after the boat had been laid up for a season. Pour it in, close the canister, and run the pump until you can smell chlorine at each outlet. Let it sit for a few hours and then thoroughly purge it with fresh water. Never had any crystal or algae growth problems after doing that.

For the "portable" charcoal filter, I bought a canister filter housing and filters from Home Depot, along with appropriate fittings that would allow me to screw a hose onto the inlet. The outlet was a section of 3/4" tubing that could direct the filtered water into the deck fill. The canister had an ON/OFF valve, which was convenient. Pretty cheap and worked great.

[St. Elsewhere]

I have been concerned about my tank corroding away for years, and never would have thought that chlorine would attack aluminum. Thanks to HUD3 for putting us on to it. I'll be charcoal filtering the chlorinated water before it goes in the tank from now on.

I did a Google search and found this bit of information to add to the aluminum tank database: http://www.guildmark.com/crumpet/Wat...0Treatment.doc

[S/V Illusion]

Which is why I and others have consistently recommended AGAINST using chlorine to disinfect aluminum tanks. Peroxide is a far preferable disinfectant, has a longer retention time, is safer and won't attack aluminum.

[gettinthere]

Hud

How much water could you treat with one filter? How often did you change filters?

Thanks for this info.

[goboatingnow]

my experience is that 15-20 years is the max life of aluminium water tanks, never like dthe stuff in general for tanks, now prefer food grade plastic

Dave

[HotRod]

To rinse your aluminium tank, use plain hot water, this dissolves the corrosion. Flush with loads of hotwater.

In general it's a bad idea to use aluminium tanks for drinking water as aluminium contains toxics that will with time follow the water...

Replace it with a stainless steel tank or a molded plastic tank made for the sole purpose of drinking water...
Why gamble with your health...

[ConradG]

A while back there was concern about aluminum and drinking water. Aluminum water bottles were plated with gold or lined with plastic. The tide seems to have changed back and now they're aluminum again. I looked into the health scare on aluminum water tanks recently and most of the info I found said it's not considdered a problem anymore. Plastics are coming into question though....next it will be stainless?

The carbon filter for chlorinated water supply sounds great. I too would be interested in hearing how many gallons (roughly) a filter might take before not doing it's job any more.

I'd also love to hear more about peroxide for a substitute. Source and dosage guidelines?

[HotRod]

There is a big difference in what aluminium alloy it is.. In bottles it's a special alloy... In a tank it's usually a soft alloy (standard plates for building) wich is not suitable for watertanks... Such plates corrode easily but the alloy used in bottles do not corrode easily...

[boatman61]

I've been of the opinion that aluminium contributes to Alzhiemers... but I could be wrong... usually am.... ask anyone..
What was the question,,,??

[ConradG]

Originally Posted by boatman61

I've been of the opinion that aluminium contributes to Alzhiemers... but I could be wrong... usually am.... ask anyone..
What was the question,,,??

I think that was the gist a few years back. Now it seems they're saying no link...

In any case there certainly is a link to chlorine eating aluminum. So charcoal filter and peroxide make sense, especially when there's salt water on the other side of one of the tank walls!

[noelex 77]

Originally Posted by HotRod

Such plates corrode easily but the alloy used in bottles do not corrode easily...

???
The aluminium grades chosen for boatbuilding are, as you would expect, the most corrosion resistant grades.
This same aluminium should be used for water tanks (5083 5086 or often 5052 which is less strong, but cheaper) Occasionally, unfortunately, builders use non marine grades of aluminium for water tanks or even boatbuilding
The biggest problem for aluminium tanks in a fiberglass boat is mounting them so that they do not get crevice corrosion. The 5 series aluminiums are not corroded at all by seawater or freshwater, but mount them on a wet fiberglass or wood surface and they can and do corrode. Chlorine does not help and is best avoided as others have said.