The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles. The solution is approved and recommended by competent health officials. It may be used in a new system a used one that has not been used for a period of time, or one that may have been contaminated.
Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete. Icemakers should be left running to allow cleaning out of the water feed line; however the first two buckets of ice—the bucket generated during recommissioning and the first bucketful afterward--should be discarded…bleach does absolutely nothing to improve the flavor of good Scotch!
1. Prepare a chlorine solution using one gallon of water and 1/4 cup (2 oz or 25 ml) Clorox or Purex household bleach (5% sodium Hypochlorite solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity. (Those are the “official” directions. They work out to 1 quart or litre of bleach/50 gallons of water , which is MUCH easier to calculate!)
2. Complete filling of tank with fresh water. Open each faucet and drain cock until air has been released and the entire system is filled. Do not turn off the pump; it must remain on to keep the system pressurized and the solution in the lines
3. Allow to stand for at least three hours, but no longer than 24 hours.
4 Drain through every faucet on the boat (and if you haven't done this in a while, it's a good idea to remove any diffusion screens from the faucets, because what's likely to come out will clog them). Fill the tank again with fresh water only, drain again through every faucet on the boat.
5. To remove excess chlorine taste or odor which might remain, prepare a solution of one quart white vinegar to five gallons water and allow this solution to agitate in tank for several days by vessel motion.
6. Drain tank again through every faucet, and flush the lines again by filing the tank 1/4-1/2 full and again flushing with potable water.
At the risk of upsetting a few people here, I do have to speak up.
First, I wouldn't do this if you have aluminum water tanks. Chlorine is incredibly corrosive to aluminum tanks. Bleach also contains a small amount of NaOH, which is also very corrosive to Aluminum. Try putting some aluminum foil in a bucket of bleach and water overnight and see what happens to it and what is this bleach solution going to do to your through hulls?
This treatment will kill everything in your tanks (except perhaps Giardia) but it calls for a very high concentration of bleach. Chlorine is incredibly lethal to fish and invertebrate life and in this instance, better to get away with less if possible. This paper suggests you can get away with less...
http://www.swcc.gov.sa/files\assets...ING PREVENTION IN DESALINATION PLANTS...5.pdf
"Combined low concentrations of copper (5 μg/l and chlorine (50,μg/l have been effective in preventing both micro and macro-fouling in over 120 seawater installations since 1987. This paper will outline the development of the technology, and demonstrate how it can be applied to the desalination industry. Recent trials with a copper/chlorine dosing unit on a reverse osmosis RO) test rig in the Gulf will be discussed."
By comparison, 1 litre of household bleach in 50 USG or 190 litres of water would contain 132,000 μg/l of Chlorine:
Bleach is a solution of 5.25% Sodium Hypochlorite which is 48% chlorine by weight.
There is 52.5g of Sodium Hypochlorite in a litre of bleach which is 48% chlorine, or 25 grams.
50 USG = 190 litres.
25 g of Chlorine in on litre/ 190 litres = 0.132 g/l or, 132,000 μg/l.
That's a lot more than 50 μg/l. I'm not suggesting 50 μg/l is the correct amount, but a concentration that is 2,600 x greater seems like an awful lot to me. And while 132,000 μg/l is set by the code referenced above, I wonder what the DFO would say about me pouring 2 gallons of bleach in a salmon bearing slough where I tie up (Fraser River). 2 gallons is what I would need to treat my 350 gallons of tankage. The local effects of that much chlorine is concerning to this fisheries biologist.
I make beer and my primary fermenter carboys get a very tenacious ring of scum that is a buildup of dead yeast, proteins and hop residue. I blast this with bleach solution with a concentration similar to the water tank treatment described by the Head Mistress and it falls away in 3-4 hours. I'd be surprised if there is a residue in my water tanks that approaches the residue on my carboys. BTW, I use and reuse this bleach solution.
Jim
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