Renting during covid-19 times

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Hi all, we have been renting out unit for past 5 years. We had good tenants more or less. Our last tenant however gave us some hard time during this pandemic. He used up all his security deposit and made us reduce his rent by 150$. Now we're are near lease renewal so I had two questions. We live in NJ

1) Can we increase a rent more than 4%?

2) were don't have their security deposit- so how can we ensure that we are covered should something break down?

Thank you in advance!

Regards, 

Chika