Thanks for this Peggy (in absentia). Here's a question though:
My ship's water container is a single stainless steel 200 gallon tank. According to Peggy's directions this means I should pre-mix 40 gallons of the bleach/water solution. This is not an easy task. Does anyone have an alternative approach?
How dangerous is bleach to copper pipes (yes, we have copper) and a SS tank? Can partially fill my tank, then add the bleach (4 quarts according to Peggy's receipt), then fill my tank with water and follow her directions? I could even add a diluted bleach mix, but I just can't see how I can pre-mix 40 gallons in one go...
JimMcGee: What inline filter do you use?
For a 200 gallon tank, the standard shock sanitization schedule using laundry grade (5%) Clorox would be ~80 ounces
of Clorox per 200 gallons. Then a soak for one hour ... 2 hours Max
. This would result in a chlorine concentration of ~10 parts per million chlorine, which is the standard dosage for municipal etc. water system sanitizing.
This is the dosage for a water system that does not contain any 'biofilm
' (calcyx - a massive bacteria colony that is living on the walls of the tank and piping. A biofilm is denoted by simply wiping a finger on the internal surfaces ... if it feels slimy, thats a 'biofilm'). Open the water tank on any 'toilet' and feel the slime on the inside walls - biofilm.
If you denote any biofilm, a single shock sanitization will usually not be effective as chlorine does not penetrate down into the film, leaving viable bacteria below the killed/stunned surface layer. If biofilm, then you need to either open the tank and hand scrub OR repeat the shock sanitization several times (eg. - repeated over several days).
The one to two hour limit will not cause the onset of corrosion to the stainless steel (weld) surface; dwell time between repeated sanitizations will allow the stainless surface to migrate more chromium to the surface - which makes stainless ... stainless.
Most of what is being bantered about on the internet with respect to 'clorox' and water system sanitization is for NEW, never commissioned, or CLEAN water systems .... systems that do not have a developed biofilm
. If there is a biofilm present, you should continue to repeat (with dwell time of days in between) sanitization until the biofilm is removed ... OR mechanically scrub the tank, etc. before 'sanitizing'.
For tank sanitization, do websearch: sanitizing + "water systems" + chlorine + "Gelman Sciences"
which is a relative 'go-to' standard for industrial, chemical/food process, municipal and bio-pharma water systems (see table 1: 10-20ppm soak of one hour (w/ 2 hour max.
That subset for 10-20ppm (table 1) will be at a rate of 40 fluid ounces of 5% chlorine (laundry grade clorox) per 100
gallons. 80 oz. per 200 gallons for ONE hour.
For a stainless tank I would recommend NOT exceeding that ONE hour limit, as if there are any 'irregularities' in the welding (blow holes, laps, undercuts, etc. ... and the weld is not ground and polished) corrosion will
form and eventually penetrate through the welded area when using 'aggressive' mixtures of sodium hypochlorite / clorox.
Rx: for 200 gal. tank - 80 oz. of laundry grade clorox per 200 gallons, ONE hour soak; repeat if biofilm until removed. A 200 gal tank 'should' have access hand-holes - use a long handled scrub brush, first.
"Maintenance dose for a 200 gallon tank (1ppm) is 8oz. clorox per 200 gallons (see 'nose/odor test' below).
To prevent the formation of biofilm: the standard 'maintenance' dose of chlorine is 1 ppm chlorine concentration ..... or 4 ounces clorox per 100 gallons, 2oz. per 200 gallons. .... OR better, is to 'work up' to that ~1ppm value by adding 'clorox' to the water, let mix (days), then open a spiggot and denote the 'faintest/barest' possible smell of chlorine in the water .... that 'barest possible' odor means 'active' chlorine is in the system. Overdosing with chlorine is harmful to the human body. Having water with the smallest
possible odor of chlorine in the water is the target. Check monthly (with your nose) and remedy ... and you wont develop a bacterial biofilm.
Other - NO water filters ON the boat (spiggot filters are OK), do all 'filtering' ... from the dock TO
the boat @ 1,0µM 99.99% efficient OR certified to remove 'oocysts
'. Filters concentrate bacteria, carbon filters accelerate bacterial growth as most common bacteria will use the carbon as a nutrient source. If possible, use carbon
filters derived from 'coconut shells' (Darco G60, etc.). Operate the carbon filter 'as SLOW as possible'
when filling the tank. A carbon filter mounted IN a water system will eventually extract most/all the maintenance ~1ppm chlorine from the (non-moving/stagnant !!!) water.
Hope this helps.