Asking the advice of your insurer can mean that it is logged as an incident - this means that it has to be declared to future insurers if they ask whether you have had any claims or incidents.
If you have accidental damage cover then you are most likely covered for the carpet. Water from a fish tank is sometimes classed as contaminated, and therefore the carpet, underlay and floorboards would need to be dried, cleaned and sanitised. Often it is just as cheap to replace the carpet. However, if the tank smashed into pieces then glass shards will have embedded in the carpet and you must insist that the carpet and underlay is replaced.
Ideally you need to check the terms and conditions of your policy, including the policy exclusions, but you can't do this if you haven't got the documents.
If you think that you have accidental damage cover then I think it's worth ringing your insurer and discussing the case.
The insurer will not cover the cost of replacing the fish unless you had special cover for them.