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Old 14-07-2020, 23:28   #1
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Is my water tank contaminated? [Video]

Hi

I had a look inside my water tank and it looks pretty gross, as you can see in the video here .

Does anyone know what the white crusty bits are and what the slimy black stuff is?

I tried scrubbing it with steel wool and then treated the tank with chlorine but with no success.

Any ideas as to what to do?
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Old 15-07-2020, 03:25   #2
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Re: Is my water tank contaminated? [Video]

Aluminium tanks?
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Old 15-07-2020, 03:26   #3
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Re: Is my water tank contaminated? [Video]

Sorry but I'm not sure. I think they might be.
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Old 15-07-2020, 03:31   #4
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Re: Is my water tank contaminated? [Video]

Looks like the reaction you get in aluminium tanks from chlorinated water. i have the same problem in my aluminium tanks and have seen it in others. I have fitted two plastic tanks for drinking water and use the aluminium ones for washing etc
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Old 15-07-2020, 03:42   #5
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Re: Is my water tank contaminated? [Video]

The white stuff is poultice corrosion of the aluminum by chlorine. The black stuff is bacteria (tank inspector).



Aluminum is an unfortunate material for potable water tanks because it is incompatible with chlorine treatment.


Have been adding bleach, or is this just tap water?
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Old 15-07-2020, 03:46   #6
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Re: Is my water tank contaminated? [Video]

The infinite knowledge of Cruiser's forum is as always overwhelming. Thanks all!

The tank is probably 40 years old and I have only had it for a year, so I cannot say what chemicals they have been using previously.

The boat is in Denmark where we have perfect tap water so I would assume it has always been filled from the tap. Maybe adding some of the product which will help the water keep.

Is there anything I can do to make it okay to store drinking water, except replace it?
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Old 15-07-2020, 03:58   #7
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Re: Is my water tank contaminated? [Video]

Quote:
Originally Posted by Frederik283 View Post
The infinite knowledge of Cruiser's forum is as always overwhelming. Thanks all!

The tank is probably 40 years old and I have only had it for a year, so I cannot say what chemicals they have been using previously.

The boat is in Denmark where we have perfect tap water so I would assume it has always been filled from the tap. Maybe adding some of the product which will help the water keep.

Is there anything I can do to make it okay to store drinking water, except replace it?

The tank is not contaminated in the sense that it is unsafe to store water. scrub it a little and add a carbon block (not granular) filter in-line if you like. Do NOT add bleach to keep the water fresh--this will accelerate corrosion. Eventually the tank will leak, but that could be many years off.
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Old 15-07-2020, 03:59   #8
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Re: Is my water tank contaminated? [Video]

On a previous boat I had a similar problem. Took the tank home and stuck the pressure washer in it. Blew dozens of tiny holes in it so it looked like a tea bag with little fountains of water leaking out everywhere.

Scrapped it and replaced with a new tank, but not Aluminium.

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Old 15-07-2020, 05:56   #9
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Re: Is my water tank contaminated? [Video]

Quote:
Originally Posted by Frederik283 View Post
Hi

I had a look inside my water tank and it looks pretty gross, as you can see in the video here .

Does anyone know what the white crusty bits are and what the slimy black stuff is?

I tried scrubbing it with steel wool and then treated the tank with chlorine but with no success.

Any ideas as to what to do?

Actually it's not that bad for an aluminum tank. The white crystalline material is a reaction between the aluminum and chlorine to form aluminum chloride. This can come from city water or from an attempt to add chlorine (bleach) to into the aluminum tank to clean/decontaminate the water system. As mentioned by others, do not intentionally add chlorine/bleach to the aluminum tank otherwise it will accelerate pitting/corrosion.
If you are filling w/chlorinated city water, add an inline activated charcoal/carbon filter. This will reduce the amount of chlorine, but typically not totally remove it from the water supply. Key to using this type of filter is to use a low water flow to help it remove as much chlorine as possible.
If you are concerned about particulate matter in the system, placing an inline filter (gross filter, 5-20 micron) in the boat before the pump and fixtures. This will stop/collect any aluminum chloride crystals before they erode pump or faucet seals. We use a "whole house" filter w/clear casing as our prefilter and works well. Easy to see when the element needs to be changed and inexpensive.
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Old 15-07-2020, 06:08   #10
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Re: Is my water tank contaminated? [Video]

If you scrubbed it with steel wool then you have likely done yourself a favor and shortened its life even more. All those small steel flecks of wire embedded in the aluminum will corrode. If you can take it out without major renovations, I would do that and pickle the insides with oxalic acid. Then rinse a few times. Heat it up or leave it in the sun to dry and I mean bone dry. Then coat the inside with an epoxy paint or a specialty tank lining.
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Old 15-07-2020, 06:44   #11
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Re: Is my water tank contaminated? [Video]

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...The white crystalline material is a reaction between the aluminum and chlorine to form aluminum chloride. ...

Aluminum hydroxide.



Aluminum chloride is fully water soluble. But yes, the chlorine participates, dissolving the aluminum oxide film that normally protects aluminum. This presets unprotected aluminum to the water.
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Old 15-07-2020, 07:10   #12
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Re: Is my water tank contaminated? [Video]

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Aluminum hydroxide.



Aluminum chloride is fully water soluble. But yes, the chlorine participates, dissolving the aluminum oxide film that normally protects aluminum. This presets unprotected aluminum to the water.

Yes you are correct the final solid ppt. is aluminum hydroxide after the aluminum chloride intermediate.


The point really was the ppt. does form/isn't harmful and a prefilter is useful to increase the life of pump/faucet seals if one introduces even small amounts of chlorine in the tank.
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Old 16-07-2020, 03:41   #13
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Re: Is my water tank contaminated? [Video]

If that aluminum tank is accessible, I would just replace it with a poly tank up front. All the gyrations to keep your water taste free and the tank intact will add up. In the long run you will wish you'd just replaced it.
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Old 16-07-2020, 04:52   #14
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Re: Is my water tank contaminated? [Video]

Hi. First, no epoxy will stick to aluminum in this condition.
Ask any professional boatbuilder.
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Old 16-07-2020, 05:31   #15
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Re: Is my water tank contaminated? [Video]

I would look into replacing the tank with a potable drinking water plastic tank if feasible. Then, going forward, use an in-line filter when filling the tank.
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