The Care Inspectorate ordered a deep clean of the building, which supports around 45 older people and 15 young disabled people, and said staff were not always following safe hygiene practices during a visit last month.
It said care and support provided during the pandemic was ‘weak’ in areas regarding health and wellbeing, infection control and staffing.
Inspectors also raised “considerable concerns” about the condition of the building and said staff were not fully aware of Covid-19 guidance in several areas, such as the correct use of gloves, visors and cleaning products.
However, the watchdog said staff supported residents with “kindness and compassion”.
It issued four requirements for the operator to put into action before next month.
HC-One said the health, safety and wellbeing staff and residents was an “absolute priority” and the feedback from the Care Inspectorate was being taken “very seriously”.
Confirming the recent deaths at the home, a spokeswoman said: “Our thoughts and sympathies are with all families who have lost a loved one from coronavirus. Every loss is felt deeply by the families and our team, and we are doing all we can to support them during this challenging time.
“As we navigate this outbreak, we continue to work closely with all the relevant authorities to contain the virus and safeguard our residents.
“We are pleased that a number of Residents have now recovered, and we continue to closely monitor the health and wellbeing of all those affected. This includes following all Government guidance in relation to infection prevention and control.
“We are grateful for the ongoing support and understanding from families, and could not be prouder of our team who continue to work on the front lines of this crisis to support as many Residents as possible to return to good health.”