I am a renter and in Canada, and insurance policies sure are not easy to read for us non-lawyer types...... No mention of aquariums, when I asked about this topic, they just sent the below which is the same as whats in the policy, I only have a small tank and landlord knows, but I imagine 20 gallons could still cause some unpleasant damage.
This is what the policy says...
Water damage exclusions.
Your Policy does not insure loss or damage directly or indirectly:
(a) caused by flood, ground water or rising of the water table, waves, tidal waves, high water, tsunamis, ice or waterborne
objects whether or not they can be attributed to earthquake;
(b) caused by gradual, continuous or repeated seepage, condensation, or leakage of water or steam over a period of time;
(c) caused by surface water, unless the surface water is a result of the sudden and accidental escape of water from a water
main, swimming pool or hot tub, but you are not insured for damage to the water main itself;
(d) caused by water that occurs when your Premises is Vacant, even if you have advised the Insurer that it is Vacant;
(e) caused by freezing of a plumbing, heating, or cooling system or an appliance that uses or holds water unless:
(1) the loss or damage occurs within a heated portion of a Building or Detached Structure insured under this Policy;
and
(2) while you or your tenants are away from the Premises for more than seven (7) consecutive days for any reason
other than receiving emergency medical treatment, you or your tenant:
shut off the water supply and drain both the plumbing system and any appliances that use or hold
water; or
(ii) make arrangements to ensure the heat is maintained at an acceptable level;
(f) caused by freezing, thawing, pressure or weight of water or ice, whether driven by wind or not, to fence, pavement, patio,
swimming pool and equipment, foundation, retaining wall, bulkhead, pier, wharf, dock or bridge