Cleaning watertank

[jzaat]

What would be the best way to clean an inaccesible GRP watertank of about 1000 litres. There is one small access hole which gives some access to one compartment, but as there are a series of baffles, the others are not.
There are black slimy things in the water, together with a very strong odour.
Have tried bleach and rinse to no effect.
Any help welcome!

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[DanTribe]

There has been much discussion here recently re the pros & cons of bleach, Milton etc. I've tried most suggestions & found the most successful to be a home brew beer sterilising solution called Chempro SDP [sodium metabisulphate].
By the way, after several unsuccessful goes, it dawned on me that you also need to clean the filler pipe, der. Bloody obvious in hindsight.
Dan

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[tcm]

We are obviously well past the gently gently Milton etc water treament.

I bet that the tank is suffering from years of hard water deposits, and until they are removed the tank will never be clean - black gunk will grip to it. Old sinks suffer the same way, and are never shiny clean until the limescale is removed. I would try empty the tank as much as poss to get a load of Viakal or similar in there, and squirt as far as possible around whilst neat, praps a garden spray thing would make sure you cover everthing more lightly than a few dollops here and there. Then chuck in some more, fill it up and leave it for a few hours. If you can extract this lot with a separate pump or fill a pipe with water and syphon into the bilge and discharge at sea rather than run crud thru the little pipes to the taps it would be better. Expect sparkling clean bilges too. moderately dilute HCl wil be cheaper and more violent but can't get the stuff in the UK. of course, loads of flushing afterwards, with a hosepipe directly into the tank.



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[MainlySteam]

How much bleach did you use? As long as the contamination is organic then bleach should fix it.

You need approx 135 ml of 3.5% (35gm/litre) hypochlorite solution per 100 litres of water ie 1.35 litres of 3.5% hypochlorite solution for your 1000 litre tank. You will find that this is enough to give the water a strong smell (despite the common belief it is not chlorine) and do not taste it as it will be strong enough to cause discomfort {I've tried!}.

On the bleach bottle it should tell you the strength - adjust the above quantity to suit eg if it is 5% use 3.5/5 times the quantity above.

The tank needs to be completely full so that the top inside surface is wetted and left for 3 to 4 hours and then drained. If you are pumping it out, then you will likely have a problem with pump and filters if there is much suspended debris. If it is possible, it may be easier to drain to the bilge if there is a lot of debris floating in the water. If you are pumping out through a galley or other tap and the tap has a filter gauze in its outlet, be sure to remove it first or it will clog.

After emptying flush well with fresh water (may have to do several times).

This is the time proven process for organic contamination, you may have to repeat it if the tank is very bad.

John

{PS Having now seen TCM's response I concur with him for any hard water precipitation on the tank inside.}


<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by MainlySteam on 19/08/2003 11:25 (server time).</FONT></P>

 

[jzaat]

Living in France so have access to large quatities of HCL.
How 'moderate' should the dilution be?
1litre/tank gives 1/1000...or is that way too rough?

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[jzaat]

I obviously didn't use enough bleach judging from your figures.
Will try again and let you know the results
Thanks!

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[MainlySteam]

And if necessary I would not shrink from using even stronger, but be careful if when you put a little of the bleach/water mix on a finger and it feels slimy, then it is at the stage were it won't do your skin any good at all if exposed to it and maybe some other things it comes in contact with like a pump internals - it won't hurt the GRP though.

Have fun.

John

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[VicS]

Please be careful. HCl (hydrochloric acid) will certainly remove limescale and quickly too but if you mix it (or anything else acidic) with hypochlorite you will get clouds of deadly chlorine gas! Also acids react with metabisulphites to produce sulphur dioxide gas which is nearly as bad.

If you do resort to HCl then have some washing soda (sodium carbonate) handy to neutralise any spillages.

A good way of getting a cleaning solution in contact with all parts of the tank is to tale it for a sail on a breezy day.

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[tcm]

Re: Chemical opportunity

oho, well, a lot stronger than that i think. You normally buy it from Castorama at summink like 30% dilution. Good thing bout HCL is that it is not gloopified/thickened like viakal so very easy to flush out. I would guess that most of the crud is sitting on the bottom. For me it has been perfectly fine to put it neat from the container, and this stuff is fine in a bucket, fine in a plastic container and fine in the tank - just a bit hissy. Incredible for cleaning primary fliters or anything in longterm contact with fresh water from a tap. Use eye protection and keep clothes away. Empty the tank mostly, and use a funnel to put in at least two litres, give it a few minutes with a cover lightly over it, then then fill up with water. I beleive the gas produced on contact with the calcium deposits is carbon dioxide - not breathable, but not lethal on contact. It will be ok to run this lot through the pipes provided you have an open tap with no little filter in it - perhaps a shower attachment with the shower thing taken off. You may need to do it more than once, but i am guessing it will be sparkling clean and white after just one treament.



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[MainlySteam]

While we are on the safety subject, perhaps I should add that the organic gases given off when hypochlorite reacts with organic material are not that good for you either in the case of prolonged exposure, but don't get paranoic about it.

John

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[tcm]

Re: Oops!

I was not aware of chlorine gas produced. Now our friend seems to have rushed off to buy some HCl. Or, he's died. Mind you - nice clean water tank, and that's the important thing. A lesson to us all eh - he should have said "how do i clean the water tank WITHOUT asphyxiating, poisoning or otherwise killing myself?" But he didn't. Tsk! Seems some people have to learn by their own mistakes...

 

[MainlySteam]

Re: Oops!

Just if you mix hypochlorite and HCl. Anyway what you worried about, youve gotta much faster getaway horse than me if we have done sumthin bad and have to make a run for it.

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[jzaat]

Re: Chemical opportunity

Great, will try that as well
Thanks!

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[jzaat]

Re: Oops!

;-)
Still alive and kicking and holding on to big bottle of HCl.
Will use it carefully...

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[vyv_cox]

With all due respect to all the other chemistry enthusiasts, my experience is that you can use chlorine in any form and strength that you wish but it will neither remove the deposits nor the taste in advanced cases, which yours sounds to be. Ultimately, mechanical means are the only answer. My tank has an inspection hatch at one end and, using a toilet brush (bought new for each occasion!) I can just reach the far end. I find that a little detergent and some vigorous brushing removes all deposits and restores fresh taste.

In your case, can you get a pressure washer inside the inspection hatch? If not I would seriously consider adding another inspection hatch. The screwed ones used on dinghies work reasonably well on a top, horizontal surface, especially if you seal the threads with silicone sealant. They are big enough to get a brush through and quite easy to install. If the answer to both of these is 'no' then you will need to experiment with various sizes and shapes of brush to clean as much as possible.

After any/all of these, go the HCl/bleach route. Suggest you install a strainer upstream of the pump and a charcoal filter after it.

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[jzaat]

I guess that would be the way to do it.
Problem is this tank is hardly accesible at all :1 small inspection hatch on the top, giving access to just 1 compartment, there are at least 3 others, with large baffles and very small openings between them.
Ergo, can clean 1 compartment somewhat( that one is already pretty clean), the others I cannot see. Without stripping a lot of the furniture to create some more inspection hatches I cannot get to the other parts...


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