@luis angel ..ok if you have space restrictions and can't use a second pump I get it. Tank size really has no impact on this, it is about water flow speed.
Here is what I have learned and have set up in my sump on the 300.
I have a dedicated pump for my UV, since I want to be able to control the water speed through the UV without effecting the return rate of water to the tank. Most UV provide a rate chart of what your are tying to achieve with the UV. Speed matters for example are you using it to control algae etc or are you using it to control and minimize health pests to your fish ? Both are achieved by different dwell times in the UV. (I will stop at that as it can go down a rabbit hole, just wanted to keep it simple right now)
So if your return pump to the tank has to be faster or slower then the parameter's of the UV flow rate, the UV is not doing much.
Also, having the UV on its own pump allows you to say one week if you have alot of green water you can adjust UV speed to deal with it and then adjust back to deal with parasites,,,
I also do not have my UV returning water to the tank, I have it taking water from the sumps last chamber and returning it to the last chamber. So when I shut off my return pump to the tank for cleaning or feeding, the uv pump and uv are working still, just in a recirculating mode and I do not run the risk of burning out the UV due to lack of water through it. Having my UV pump pull water and return water to the last chamber allows my return pump to the tank to deliver the UV'ed water without me having to have a pump on the UV that can handle pushing water 5 feet to the tank..so a smaller pump for the UV
In your case you could pull water from mid sump and return to same chamber so that it is recirculating and you do not run the UV without water.
Also for cleaning, having two pumps allow you to clean them independently and when you have to do Maintenace on the UV it does not stop water to the tank.
I hope this make you think...preparing for the future is one thing I learned about this hobby..simple is better...along with easier.
I am here for you...