They eat at different rates since no one answered you. depending on the chemicals or minerals in the water...Hope that answers your question. "Depending on how much you know about your water heater’s anatomy, you may have heard of the anode rod. Sometimes called the “sacrificial” anode rod, its job is to divert corrosive action away from the tank walls and to the anode rod.
Since the anode rod’s job is to corrode, you obviously need to replace it regularly when it starts to give out – otherwise your water tank walls will start to corrode in its place. In fact, replacing your anode rod when you’re supposed to may even increase the lifespan of your water heater, preventing costly breakdowns and saving you from needing water heater replacement.The condition of your anode rod (and whether it is time to replace it) depends on your water quality, how much you use your tank, the temperature of your thermostat, and, of course, the quality of the tank itself. Note: if you soften your water with sodium, this will lead to a shorter life for your anode rod. When using an anode rod, be aware of all the factors that affect it so you can keep your water heater in top working order.
There are a few different types of anode rods, all with their own unique advantages:
Magnesium Anode Rods – an excellent choice for anode rods, magnesium anode rods do corrode at a faster rate than other materials. However, dissolved magnesium in water can offer many health benefits.
Aluminum Anode Rods – aluminum rods are the least expensive anode rods and create the lowest voltage during the sacrificial process. As a result, they corrode more slowly than other anode rods. Most manufacturers use aluminum anode rods as standard equipment. Flexible aluminum anode rods also exist that are designed for limited spaces where a straight anode rod would not fit.
Aluminum / Zinc / Tin Anode Rods – if your water heater smells like rotten eggs, you should consider an aluminum/zinc/tin anode rod. This particular combination of metals is often used when foul odorsare present in the water, aszinc is a natural anti-fungal element that can help mitigate the growth of iron bacteria which can cause that rotten egg smell. Zinc oxide and zinc compounds are indigestible to micro-organisms such as bacteria.
Hot Water Outlet Anode Rods – hot water anode rods are perfect to use if your water heater doesn’t have a separate anode rod inlet port, or if your old anode rod is impossible to remove. There are aluminum/zinc/tin and aluminum hot water outlet anode rods. Hot water outlet anode rods often include built in heat trap nipples designed to keep any cooling hot water from entering back into the water heater and potentially cooling the water down" un quote....