Help on Power conditioner

In my house the Power having a fluctuation and found voltage variation between day and night times. Here the voltage 230v and day time we are getting 210v and night time 220-230v.

I have pass lab xa.5 mono blocks hence I am worried about the safety. So, You all suggest me the best stabilizer or conditioner with surge production to buy.

One of my friend has informed me that Pass is not recommended any power stabilizer, conditioner or re generators. Is it correct ?

Any one using these kind of accessories for Pass lab products? How the performance
of the amps using these accessories?

I am expecting suggestions and advise from you all.

Thanks in advance.