Broken dishwasher and rental increase

[Wendy Lam]

Hi all, hoping to get some good feedback on my situation.

This is my first rental property, purchased in fall of 2021. Tenant has lived at property for 20+ years. Their previous rent was about 700 under market value, I bumped it up but still 400 under market value. Always timely on rent, and takes care of the property. When I purchased the property, the dishwasher in the unit was already broken. The previous owner did not replace it knowing they would sell the property soon. 

I am ok to purchase and install the new unit ($400 + $150 install), but given that they're still under market rent, I wanted to negotiate a rental increase with the dishwasher. Given that renewal is 4 months away, what's the best way to approach this? I'm thinking +$50 per month effective on their renewal.