Tenants complain about vent cleanness

[Robin Evans]

Dear BP friends, hope you all had a great Thanksgiving holiday! A tenant of ourshas just complained today about vent cleanness after he lives in the unit for 10 months. He sent us a pic of the ceiling after bathroom exhaust vent is removed that shows an accumulation of dust and says it is impossible that it got that dusty in the months that they live there. He then further complains all air vents in the house are dirty and sort of implies we need to get all vents cleaned. He mentioned the situation is not healthy to his several-month-old baby. 

The previous owner did hire a cleaning company to do a deep cleaning before moving out (vent is cleaned or not is not mentioned to us). We didn't clean the air vents after we bought the house and then just did some general cleaning before we rented it to the tenant (about one month after we took over the property) . We did do a thorough move-in inspection with the tenant before moving in and we signed the move-in inspection sheet. Everyhing was marked "good" by the tenant on the sheet, including exhaust fan. Air vents for the whole house are not mentioned on the sheet and not part of the inspection. At the time, we didn't think tenants would complain about that (and this is the only tenant who has complained about it of all our 10 units so far). 

Previously he also complained about us not weedwacking (which we have been doing) and fall leaves getting into his garage that brought bugs. It goes on and on.... This tenant of ours is not our favourite.  Our neighbour there has complained about him being loud.

 Here are our questions. 

1. Do you guys usually clean air vents before renting the unit out? Is it necessary? I googled and EPA does not recommend that the air ducts be cleaned routinely, but only as needed

2. How to respond to the tenant's complaints about air vents?

3. His one-year lease ends end of Jan. 2023. We are thinking about giving 60-day notice and terminating the lease. Do we need to give a reason? 

Any input is greatly appreciated ! Thank you very much!