Full or empty water tank in tropical temperatures

[Hasbeen]

My boat was in the high tropics for 12 years, & the tropics for 14 years. My water tanks were welded polypropylene sheet glassed outside, which may have helped, but they had water in them at all times. There were periods when I was ashore for months at a time, with out the water going off.


It may have helped that they were directly filled with rain water, although I'm not sure that was not detrimental. They had been filled with Sydney Oz mains water for some time before I went cruising, & that appeared to be no problem either.

[a64pilot]

So far I’ve not had an issue with the water in the tanks, even though for the last 8 months, only Watermaker water has been used.
I do believe that I have a growth issue in my lines however as some have dark stained.
I’m leaning towards maybe shocking the line with a 5 gl bucket and Peggie’s concentration of bleach, and not putting bleach into the tank.
I’ve had advice from what I consider likely a water treatment expert, and his recommendations to shock a water tank vary very differently from Peggie’s.
While I’m sure her recommended concentration would likely kill anything, for my aluminum tanks I think it may be excessive, even for short term exposure.
Attached image is concentration amounts to equal set PPM. It may be a lot less chlorine than many may think they need.
For instance if your just wanting to treat to municipal levels, not shock, it’s only 1/3 of an ounce per 100 gls of water.
I thought it would be much more than that.

[Bulawayo]

We used to do quite often. We fitted inspection access hatches. We would drain down our tanks completely and physically towel them dry. The drain down would include a bleach treatment of all the lines as well. We would repeat a bleach rinse before refilling.

[opusnz]

I have left my boat in the tropics many times and never noticed a problem with water in the tanks, even after many months. I really wouldn't worry about it unless you have plastic or bladder tanks which can sometimes make the water smell like chemicals over time.



If I leave my boat in the water, I usually try to leave the tanks empty...only because my boat will float higher and expose more waterline. It has nothing to do with water quality.

[sailores35]

Originally Posted by Eder

I filled mine...I'll treat it with some bleach when I get back to it once I get the water maker running. Partially damp large shaded tank could be scary after 6 months.

Be sure you do not have an aluminum tank.

[sailorboy1]

There’s science and then there’s voodoo

For this subject science is proven and voodoo is only needed if your tanks have zombies

[becrux]

Originally Posted by Singularity

FWIW I don't buy the BOD concept in this application...I mean the tank isn't a swamp to begin with, but anyhow:

Supposing 5 gallons 30% H2O2 sanitizes 1,000 gallons water...
Probably screwing it up weight v volume, but...

1 gallon is 3785ml
30% H2O2 contains .3g H2O2 per 1ml
.3g x 3785ml = 1.135kg H2O2 per gallon of 30% solution

It's given that 5 gallons 30% H2O2 (which contains 5 x 1.135kg = 5.68kg H2O2) sanitizes 1000 gallons....5.68kg H2O2 needed for 1,000 gallons

So 150 gallons is 15% of 1,000 gallons.
So 15% of 5.68kg H2O2 is 852grams H2O2...we need 852g H2O2 to treat 150 gallons water

12% H2O2 contains .12g H2O2 per 1ml
A gallon is 3785ml, so
1 gallon 12% H2O2 contains .12g x 3785ml = 454g H2O2....but we need 852g.....so we need just under 2 gallons of 12% to treat 150 gallons water.

There's something to be said about a career pilot's typically superlative ability to synesthetically shoot math accurately from the hip.

Perfectly accurate, but a little overkill.
Let's keep it simple. Shortest path to the right answer...
Supposing 5 gallons 30% H2O2 sanitizes 1,000 gallons water...
To sanitize 15% of that amount you need 15% of 5 gallons or .75 gallons.

If you use 12% H2O2 instead of 30% you need .30/.12 times .75G = 1.875 gallons.
Same answer, shorter path.

As you point out later, the amounts are based on a supposition that the quantities given will do the job. Thanks very much for the CDC quotes and links.

[becrux]

Originally Posted by Singularity

If hydrogen peroxide in solution is the goal, arguably the easiest/cheapest method to get high concentrations is to use sodium percarbonate powder (aka Oxiclean, aka sodium carbonate peroxyhydrate). When added to water it breaks down into hydrogen peroxide, sodium, and carbonate. If the tank/plumbing material can tolerate hydrogen peroxide, you can really nuke the tank/plumbing system with just a little Oxiclean, which is easy to keep a lifetime supply on board for a few buks (just make sure the content is exclusively sodium percarbonate [+/- sodium carbonate] without artificial scents or other stuff added). No chlorinated anything involved. I'm a huge fan of the stuff. It does leave a little white residue (sodium carbonate ash) when used, but this is inert and can be safely consumed in reasonable amounts as would be used in tank sanitizing (sodium carbonate is used as a food additive).

Excellent suggestion. In the wine industry we refer to this stuff simply as "percarbonate" or sometimes "prox". It's pretty much the standard for cleaning SS tanks. (Larger producers use soda ash.)

>It's food grade - no additives.
>I buy it in 25 kilo bags for about US$65
>At about $1.20/lb, it's way cheaper than Oxiclean.
>My wife uses some for the laundry.

Caution: DO NOT use this on aluminum. It will get ugly.

I have never seen any sodium carbonate residue, possibly because I never let the tanks dry out until they have been well rinsed. When rinsing at the winery or on the boat, I add a bit of citric acid (about $95/50lb.) to passivate the stainless and neutralize the high pH. Not sure I would leave this in a SS tank for an extended period because of the high pH. Overnight is fine at the winery. My boat's tanks are GRP, except the fuel tank, so not a problem for me there.
But it certainly makes an excellent beginning-of-season flush. For my 120G tanks, a cup of the stuff feels about right. I put it in, fill the tanks, run the taps, and let it sit overnight. Waste it, rinse with a little citric - fill and dump right away, fill again, and go out.

[becrux]

I omitted saying to dissolve the prox in warm water first. It needs a little help to dissolve.

[S D Sailor]

+1 for full & capful bleach.
Since 2015 I have left Luna Sea for 2 to 3 months in Belize & Rio Dulce with tanks full and a couple tablespoons of bleach in each hundred gallon tank and 1 tablespoon in the 35 gallon tank; all 3 are fiberglass.
I have never tasted the bleach and I’ve never had a critter or growth problem…
As we used to say in the Navy “works fine, last a long time…”. ;-)

Best...