Call your auto insurance company. Most now offer many lines of coverage or have a sister/parent company that can offer it. Discounts are available with multiple vehicles & policy types.
General liability coverage is just what it sounds like. It covers acts of god, coverage for your person & family, and coverage for people working on your property. There are many riders you can add on a homeowners or renters insurance; Scheduled personal property endorsement - computer/electronic equipment, jewelry, and pets. There are exclusions for dangerous animals along with inclusions for such things as fish tanks. The tank is covered under the general liability portion of your policy. The damages they can cause are usually not. A rider must be requested and added to the policy.
Bottom line, you need to tell someone you have a tank or tanks. It needs to be specifically written on your policy and not violating any rental agreement. I don't know the specific rider, but I know the general coverage will not cover loss incurred from tank breakage as it is not a "permanent" structure in the home.