If the flow got weaker I don't think it is related to the tanks you have under the sink. In my opinion it has to do with  scale growing on your tap. To get rid of it remove the taps filter and place t in vinegar for a couple of hours and watch the magic. If you think t is the filter tanks the thing is you have to open them and remove the filter from the inside, be-careful it is pretty difficult to unscrew them. they need to be replaced once every half a year. Usually these systems are made out of three tanks , just take them with you and you can find new ones at any diy store.

This is how they look like: