Treating Fresh Water

[HopCar]

Bill E, the active ingrediant in Clean Tabs is Sodium Dichloroisocyanurate.
It is an oxidizing agent like Sodium hypochlorite.

On the subject of corrosion of aluminum tanks, this is what the Clean Tabs FAQ's say about it:
"Will it corrode like bleach?All the products are not corrosive when used as directed and are completely different to bleach. Bleach is hypochlorite which is a harsh corrosive chemical and must not be used in connection with drinking water or a water storage system."

[svtrio]

WHO and the U.S. CDC have considerable documents about treatment of drinking water, but the link below gives an easily understood overview of treatments, including iodine.

<http://en.wikipedia.org/wiki/Portable_water_purification>

As for the interaction of iodine, hydrogen peroxide, etc. on aluminum, the diluted amounts used for treatments suggest that long-term damage doesn't seem likely, but Google searches can point to considerable technical reading on the subject.

Roger

[Bill_E]

With all due respect, I wouldn’t use Clean Tabs in aluminum tanks. Nor would I use bleach. I’ll try to go through the whole story so if you care, bear with me, if not, go read something that will be more fun.

Both dichloroisocyanurate (Clean Tabs) and hypochlorite (bleach) work by releasing chlorine into the water. The chlorine is a strong oxidizer and that action kills cells (bacteria, algae, fungi, etc.). There are several mechanisms for the kill. The problem comes about with the aluminum. First, aluminum is a relatively reactive metal but it forms a pretty tough oxide coat that protects the bulk aluminum. The free chlorine in the water will react with the oxide making Aluminum chloride, which is not as tough. It will crystallize and some of the crystals will break off the surface exposing more of the aluminum. The reaction, substituting chloride for oxide, will occur preferentially at microscopic defects in the aluminum. Eventually this will lead to pinholes. If one were to put a chlorine source in the tank for a very limited time and then wash it out completely the amount of aluminum chloride formed would probably be small. The big problem comes from constantly putting small amounts of a chlorine source in the tank. A little bit at a time over a long, long time equals a significant problem.

There are two common oxygen based disinfectants (oxidizers), peroxide (usually in the form of hydrogen peroxide) and ozone. Both of these and the combination of them are used in many municipal water treatment systems. The oxidizing potentials of both of these are stronger than chlorine. But the important fact is that their reactions with aluminum or aluminum oxide produces only aluminum oxide or aluminum hydroxide, depending on pH and maybe some other conditions. I am pretty sure that aluminum hydroxide is the result of anodizing aluminum to passivate it. But of course the aluminum hydroxide generated in the anodization process is controlled and evenly put on the surface. Although you can purchase an ozone generator, I think that properly installing it on a boat along with the electrical demand, makes it untenable for most of us.

So, for me, I’m going to resort to hydrogen peroxide in my tank for shocking it. I will also continue to filter all of the water that goes into my tank to remove the chlorine from municipal water systems. That means I’m relying on cleanliness and care to avoid bacteria rather than having an active chemical disinfectant in my tank at all times. I’m still a little uncertain about the concentration of hydrogen peroxide and time needed to properly shock my entire fresh water system. But I have a plan that may be a bit of overkill that I think will work.

We tend to use five gallon plastic containers of water for drinking most of the time rather than drawing out of the main tank. And we keep spare gallon milk jugs, etc around for more drinking capacity.

I will admit that I owned my Sunbeam for a couple of years before I thought about the aluminum tank problems and during that time I’m sure I ran a few hundred gallons of chlorinated municipal water through the tank and I doubt if the previous owners really considered this issue. One of the reasons that I’m sensitive to this is that I found that my stainless steel holding tank had many pinholes in it. The PO attempted to fix it with fiberglass and resin but I ended up having to get a new tank welded up and am presently in the process of installing it. Admittedly black water is more corrosive than fresh water. I would sure hate to have to replace my freshwater tank because it would mean taking up a huge amount of the sole.

I hope this discussion is useful and not too pedantic.

Bill

[ReMetau]

We don't treat the water in our tanks, but we do the jerry jugs otherwise the sun causes algae growth. We usually add a small amount of bleach to each jug if we aren't going to use it right away.

We had somebody suggest adding cheap Gin to the water. I think we did this for a bit and if I remember correctly it did work. Also it has the benefit of quickly killing caught dolphins so blood doesn't get everywhere.