Thoughts on rent increases, should i raise immediately or....?

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For a little context; 

I took ownership of a Triplex in the greater Montreal area about 7 months ago, the property at the time of acquisition was fully rented with leases set to end in June of 2017. The market rent in the area is at 755$, 2/3 units are well above market rent, with both renting above 780$ however the 3rd unit is far below the rate, renting at 700$. Now the tenants in this unit had arranged to do the lawn around the property to compensate for the lower rent, the property is 11,000Sq ft and as such has a decent amount of lawn to be cut during the summer and spring. 

My question is: Should i leave the lower rented unit at the below market rate rent and continue with the tenants providing lawn care or should i raise them to benefit my overall cashflow? The property as a whole is renting at  the market rate rent ( Unit 1: 700 + Unit 2: 780 + Unit 3: 785 Average = 755 )

Sidenote: the tenants are good tenants, never had issues with them and they even preform their own repairs as they are quite handy.

Would love to hear your opinions and similar experience!