Uh-oh... it'srarely if ever bacteria that causes the "rotten egg" odor in hot water....and the last thing you want in it is bleach! In fact, the directions for recommissioning the fresh water system specifically say "Before beginning, turn off the water heater at the breaker and do not turn it on again until the entire recommissioning is complete" (iow, ALL the bleach solution has been flushed out of the system). However, I don't think 1 oz/50 gallon can do any harm, or for that matter any good. 1 gallon is 128 oz...so 50 gal is 6400 oz of water. 1 oz of bleach would be a ratio of 6400:1. You'd get as much benefit from just thinking hard about it! Your .5 oz/5 gallons results in a ratio of 640:1. I suspect you could probly drink that without a harm to your health.
A little "marine water heaters 101" might be useful:
Most marine water heaters have have ANODIZED aluminum tanks. The anodizing wears off over time, resulting in the "rotten egg" odor that's ONLY in the hot water. The only real cure is a new water heater.
Water heaters that have glass lined tanks have a replaceable anode that protects the inside of the tank against corrosion from acids in the water, stray electrical currents, etc. Glass lined tanks, when the water heater is being built, are heated up red hot. Then glass powder is sprayed inside the tank and it adheres upon contact. However, it doesn't cover every single crack and crevice inside the tank - it should, but in actual practice, it doesn't. The purpose of the anode is to protect those spots inside the tank that have not been glass-covered from rusting away prematurely. The anode is eaten away, rather than the tank being eaten away. Kind of a backup to the glass lining.
The anode is a magnesium rod, about 3/4" in diameter that is attached to the inside of the hot water "out" nipple, via a plastic coupling. It is electrically isolated from the fittings and from the tank. It extends all the way across the inside of the tank, stopping just short of the other side. There is an iron rod in the center of the magnesium that supports it, the iron being stronger than the magnesium. As the magnesium is eaten away and the iron rod exposed, there's a chemical reaction between the water, the iron and the magnesium that causes the "rotten egg" smell. Replacing the anode and flushing out the tank will usually make the foul smell go away.
Glass lined water heaters are more expensive than those with metal tanks, but they last upwards of 25 years.
Check out the Raritan water heater (and don't be spooked by the list price!)
Raritan Water Heater
--Peggie
