It's time to replace my anode rod and I'm not sure what type I should get (Magnesium, Aluminum, Combination, or Powered). I have a well and use a water softener. I have a high iron content (orange stains in toilet tanks and in showers) and I've just started adding rust-remover pellets to the softener. There is also a very slight rotten-egg smell to the water. I don't think the anode has been changed in many years. What type of anode rod should I get?
It depends on how much you want to spend, how old your water heater is and what kind of water you have. The aluminum rods are usually the cheapest followed by magnesium. The combination rods I don't have much faith in as the least noble metal is eaten away first. powered rods that will last a lifetime are very expensive due to the platinum wire used. Your water is high in mineral content the Iron and possibly sulfur (rotten egg smell) so Magnesium would be the most cost effective. (with Low mineral content Aluminum would be the way I would go). I did have a P wire system on a metal boat instead of anodes it worked well and I no longer had to change out several a year but a water heater I think P wire systems are overkill on a home system. Make sure to turn off the water heater and flush it when installing the new anode this may help reduce the smell. Water heaters tend to last for ~10 years some 15+ so if you are at the upper end of the life scale you may want to go with the cheaper anode. Once the damage is done there is no way to reverse it.