An aluminium anode can be used if your water supply is of poor water quality in order to extend the life of the tank. You can request a “hard water” aluminium anode to be fitted to Aquamax glass tanks as part of an Apricus solar hot water system; and if ordered through Energy Matters, there is no extra charge.
Anodes aren’t really an issue with rainwater tank water, but are definitely recommended for use with bore water, or poor water quality. Melbourne and Sydney water is of a good to very high quality. Adelaide is of very poor quality. Tasmanian water is regarded as the best in the world!
To combat hydrogen build-up, all water heaters have a pressure and temperature relief valve fitted to Australian Standards. You simply pull the lever and “purge” the tank for 30 seconds if you have been away on holidays for two weeks or more. This will dispel any hydrogen gas leeched from stagnant water.
If the system is used every day, the hydrogen does not separate from the oxygen in the water molecules, and this does not occur. Regardless, all tank manufacturers recommend you purge a system at least once every 6-12 months.