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Old 22-08-2008, 17:58   #16
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Originally Posted by hellosailor View Post
I suspect we normally use the white translucent poly tanks in the US, because it is easier to inspect them. Any type of mold or growth on a black surface would be hard to see--but on a white one, it stands right out.
The reason black tanks are black is so that "mold or growth" will not grow inside them.

But, of course, it may be entirely different in the USofA - I cannot claim to be an expert on how it differs from the rest of the world in the above respect .
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Old 22-08-2008, 20:27   #17
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I understand, deprive algae of light and they won't grow. But there are other things that can and will grow, in drinking water, in the dark. I've caught black stuff (probably a mold or fungus) growing in a water pitcher, left in a refrigerator in the dark and cold for a month. Against a black background--I'd have never seen it. Against a white background, it is very easy to spot.

Never had had plankton or algae in the refrigerator, though.<G>

It is possible that there is a USDA requirement that tanks certified fit for drinking water be a certain color, stranger things happen here.
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Old 22-08-2008, 20:37   #18
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I've caught black stuff (probably a mold or fungus) growing in a water pitcher, left in a refrigerator in the dark and cold for a month.
Have you checked that the little man inside the refrigerator who turns the light off and on has not died or was off work sick that month.

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It is possible that there is a USDA requirement that tanks certified fit for drinking water be a certain color, stranger things happen here.
I would be pretty confident that there isn't as there are hordes of US manufacturers of black polyethylene tanks for potable water storage, including Ronco Plastics that Delmarrey linked to in their recreational marine range.
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Old 22-08-2008, 21:52   #19
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Not all critters that can grow in a tank require light.
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Old 23-08-2008, 05:49   #20
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Not all critters that can grow in a tank require light.
Of course that's correct David but the comment that I responded to was Hellosailor's "Any type of mold or growth on a black surface would be hard to see--but on a white one, it stands right out." so black tanks were not used (referring to the USA, I think).

The main tank wall fouling organic is algae. As far as I know all algae, unless artificially genetically modified, rely on photosynthesis so they obviously won't grow in the dark. They therefore cannot foul dark tank walls so are not needed to be able to be seen. They obviously can foul translucent tank walls if the tank itself is not kept in the complete dark.

Molds (which includes fungii) do not depend on photosynthesis and so obviously will grow in the dark - bread mold being a common example, but I have never seen an example of molds being a problem fouling walls of a dark tank. That probably because they depend on other organic matter dependant on photosynthesis (but often dead) in which to live for energy so they cannot survive on dark tank walls. In fact, it may be that no molds will live under water (even though they need water to survive) but I don't know that, maybe someone does? EDIT In fact there are, have just thought of some fungi that do eg those parasitic on fish.

Some bacteria (among the non phototrophs that don't rely on light as an energy source) will grow in the dark - quite obvious really because they will even grow inside us. Some living in water can make you sick eg cholera, typhoid but that whether your tanks are light or dark and you can't see them so again tank colour makes no difference to identifying their presence. Bacterial slimes exist and at least some will grow in the dark (including inside our bodies) but I have never seen them on the walls of a dark tank, again I assume because there is nothing there for them to get energy from.

Some protozoans (which includes the amoebae, flagillates, etc) will grow in the dark but they need something to eat. Some living in water can make you sick eg giardiasis, amoebiasis but that whether your tanks are light or dark and you can't see those whatever the tank colour - I suspect, but don't know, that the pathogens will not multiply in the tank, they need to be in you or an animal to do that (maybe someone knows). Some larger protozoans can reach a millimetre in size so can be seen if there are enough of them to become obvious. But they will only be there if taken in when filling the tanks from some swamp and will be among the mosquito larvae, worms and other assorted wildlife collected with them and who will soon gobble them up .

Getting away from just the tank walls - dark tanks are widely used for storage of rainwater and from springs, etc and I have never known them to be regularly cleaned (in fact I have used water from many that I know have never been cleaned in the decades they have been in service). I have only heard of problems when they have become contaminated by pathogens in the collected water not from anything that has grown in the tank. Pathogens cannot be seen whatever the colour of the tank. For all of molds, bacteria and protozoa, being those things some of which can live in the dark, they depend on organic matter or carbon sources for energy. Algae is one of the major sources of that energy so keeping tanks dark so that it cannot survive (algaes relying on photosynthesis) removes the major energy source for the single celled critters.

Our own tanks are metal and so are completely dark - I have never found anything growing inside them over their current 12 year life. The interiors are lined with white epoxy so as Hellosailor says, anything will stand out - it stays white.

We are in good company because all the world's shipping fleet uses dark tanks and I have never heard of anyone suggesting that they should have translucent walls so that one can see what might be growing on them . I assume everyone in recreational boats that has translucent tanks (which may include moulded in tanks of fibreglass if they do not have a complete barrier to light in them such as a plywood core) keeps them in the dark so I can only assume that if you get growth on the walls, especially if algae, that it is not dark enough.

Thats more than enough from me for this thread.
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Old 23-08-2008, 06:05   #21
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Quote:
Originally Posted by MidLandOne
... The main tank wall fouling organic is algae. As far as I know all algae, unless artificially genetically modified, rely on photosynthesis so they obviously won't grow in the dark ...
Thanks for the informative post MidLandOne !

I’d never considered GM algae, but your comment led me to this:

Photosynthetic Algae Altered To Grow Without Sunlight
“... Scientists have now found that by inserting just one gene that catalyzes glucose transport into the diatom Phaeodactylum tricornutum, the organism can thrive in the dark, getting its energy exclusively from
the glucose ...”

Goto:
http://www.unisci.com/stories/20012/0615013.htm
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Old 23-08-2008, 09:13   #22
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We had to redo our fiberglass water tanks and even with finding materials rated for food use to coat the insides with, we were suspicious. Also with every boat we’ve ever had the tank water tasted terrible. We purchased a seagull water purifier system made by General Ecology. I don’t know if you can believe everything they say about their filtration system, but the water tastes wonderful. We’ve been using it for several years now.
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Old 23-08-2008, 09:20   #23
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On my Catalac, I had stainless tanks for potable water. At the beginning of the season, I would give a strong cleaning dose, of puriclean which was a cleaner that needed a double rinse out before drinking. I also used a couple of aquatabs per fill up.

I also had a Jabsco water filter.

The water was better tasting than that from the taps at home.


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Old 23-08-2008, 17:02   #24
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The comments that black tanks are not used in the USA for potable water prompted me to have a quick look around. I can't resist posting the advice from Bailiff Enterprises Ltd, just one of many US manufacturers of tanks (they make black and translucent potable water tanks, as well as tanks for many other services) -

When considering what plastic water tank to buy, you should take several factors into account. If the tank will be exposed to sunlight, you will want a tank that is opaque (not the natural milky white color of polyethylene). The dark color will block out sunlight that would encourage the growth of algae and bacteria. The most common solution is to use a black water tank.

The link to that is http://www.plasticstoragetanks.com/water_tanks.htm .

It seems black tanks may be a little dearer and ss much dearer again so it may be that many US production boats use the cheaper translucent - but I don't know that, I have only been exposed to custom or semi custom built US boats.

As a general comment I suspect that any tank in "normal" sized fibreglass pleasure vessels is exposed to light at some level or another due to the translucency of the hull and the lack of space allowing the tank to be located away from that.

Talbot, in my opinion, outlines one ideal solution for such boats.
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Old 23-08-2008, 17:33   #25
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Since the entire boat is new, it may be the hoses as well as the tanks that taste bad. I would go through the whole bleach "shock" treatment as per Raritan's Peggy Halls advice here:
http://64.233.169.104/search?q=cache...ient=firefox-a
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Old 23-08-2008, 22:22   #26
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Quote:
Originally Posted by MidLandOne View Post
The comments that black tanks are not used in the USA for potable water prompted me to have a quick look around. I can't resist posting the advice from Bailiff Enterprises Ltd, just one of many US manufacturers of tanks (they make black and translucent potable water tanks, as well as tanks for many other services) -

When considering what plastic water tank to buy, you should take several factors into account. If the tank will be exposed to sunlight, you will want a tank that is opaque (not the natural milky white color of polyethylene). The dark color will block out sunlight that would encourage the growth of algae and bacteria. The most common solution is to use a black water tank.

The link to that is http://www.plasticstoragetanks.com/water_tanks.htm .

It seems black tanks may be a little dearer and ss much dearer again so it may be that many US production boats use the cheaper translucent - but I don't know that, I have only been exposed to custom or semi custom built US boats.

As a general comment I suspect that any tank in "normal" sized fibreglass pleasure vessels is exposed to light at some level or another due to the translucency of the hull and the lack of space allowing the tank to be located away from that.

Talbot, in my opinion, outlines one ideal solution for such boats.
I would suspect that is why sewage tanks are black.
As for light passing thru the hull. That maybe true for boats under 36' (11M) but most boats in the 40' and above are fairly thick w/o light transfer. I know that mine is dark in the storage spaces even on the sunniest days.

BTW it is recommend that vessel (& RV) owners treat their tanks with a little chlorine once in a while.
Just some comments, not criticism!

Maybe this will answer a few questions. It's directed at ships but is still applicable.

http://www.uscg.mil/directives/cim/6...CIM_6240_5.pdf
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Old 23-08-2008, 23:46   #27
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As for light passing thru the hull. That maybe true for boats under 36' (11M) but most boats in the 40' and above are fairly thick w/o light transfer. I know that mine is dark in the storage spaces even on the sunniest days.
Yes, I wouldn't be sure what size/displacement fibreglass sailboat the hull layup typically becomes thick enough to exclude enough light to make growth on translucent tanks and hoses a non issue.

Do you have translucent tanks exposed to the hull plating and have no problems?
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Old 24-08-2008, 15:38   #28
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They're probably made locally down here, but "food grade" is always debatable with black plastic, in my experience.
Some alkali solution like bicarb followed by Milton's then more Bicarb then a washout and dump for the watertanks should fix it. Getting the PVC resins and plastisols and other gunge out for good might take some more extreme chemical violence, though! Be prepared to repeat the process every few days for a week or so.
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Old 24-08-2008, 18:16   #29
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They're probably made locally down here, but "food grade" is always debatable with black plastic, in my experience.
ANY plastic is suspect unless certified for food, water, not just black.

But as you appear to be a South African I can understand where you are probably coming from on this .
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Old 24-08-2008, 22:02   #30
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Yes,
Do you have translucent tanks exposed to the hull plating and have no problems?
Yes I do have the translucent white tanks that sit under my solon seats next to the hull. I've not yet had any growth in them. But, they are filled with city water which is chlorinated. The tanks also have large inspection ports in the top just in case there is a problem. They are the INCA brand.
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