Just read an interesting article about growing reefs using steel structures with low voltage current. This would be an interesting change in tanks. Here's the full story:
http://www.bbc.com/future/story/20150506-why-we-should-electrify-the-ocean?ocid=global_future_rss
http://www.bbc.com/future/story/20150506-why-we-should-electrify-the-ocean?ocid=global_future_rss