Mold in unit, tenant claiming rent decrease - how to proceed next

[Fedor Volkov]

Hi BP community, 

Running into an issue with one of my tenants in a property that I'm house hacking. Few weeks back I asked them if they had any issues with their property including plumbing and we found a leak under the kitchen sink that apparently was there for a while (tenant never reported it to me) and now I am arranging services to make the plumbing repair. A week later I get an email from the tenant asking for a rent discount because they caught an eye infection while cleaning the mold herself (citing that they got a fungus infection). 

As a landlord, my responsibility is to respond to tenants complaints and to fix things as soon as possible, which I'm doing, however the leak was there for a while and was not reported to me timely and now I have mold that will likely cost me a lot to remediate + tenant claiming a rent relief. 

Do you have any advices on how to proceed in this situation? They've been good tenants overall and this is a bit of a surprise to me. 

Thank you