If he's licensed then I wouldn't worry. Just be upfront with the insurance company so they can tell you what they can and will cover under what circumstances so you can accommodate accordingly. Your build pics/receipts should be enough for them to determine an adequate policy for you.

I deal with ING/INTACT, and when setting up mine, they said I am fully covered for my tank and house and any damage it may cause to the house, this without a rider. They won't cover a fish dieing on its own, but will cover tanks and all contents if the tank leaks and causes damage to system or house, or if it just lets go, destroying everything around.

Great question though, something everyone so make sure they are covered for. In my case, I think I am lucky, as I did call to do a rider and then found out I didn't need one.

Thanks to my wife, she handles the insurance for everything. She is a BI adjuster for a larger Insurance Firm, so I leave this to her, as she knows how to talk the talk. HEHE.