Having spent many years as a tenant, always having tenant's insurance, and now being a landlord of 2 properties, I can see where he's coming from about the tank, but not the rent increase ...
He may not want the 70g if it's not on a ground/concrete floor, but that's just a thought as I don't know your situation
From a landlord's perspective, and humidity aside, I wouldn't want the headache of going through all the cleanup after a leak, regardless of tenant's insurance
For example, if the rental property needs to be vacated during repairs from water damage, the landlord will be out of pocket until the premises are again habitated
Plus, the insurance company will go over everything damaged that wasn't new, and pro-rate repair costs
We had an issue I won't go in to that cost us, out of pocket, $7,000, including 2 months of lost rental income
No matter what you decide to do, get tenant's insurance. It'll cover all your personal belongings in the event of fire and theft. Flood is stupid fine print, so ignore it
Good luck with whatever you decide to do bud
