The previous homeowner put in a GE SmartWater reverse osmosis filter under the sink, which is attached to the cold water. It was experiencing low pressure (the sink-top valve would spurt water for less than half a second and then drip). I purchased new filters and a new pressure tank, since the existing tank seemed to have a leak in its bag (diagnosed based on weight, and unwillingness to hold pressure from a bike pump).
I thought for sure replacing the tank would resolve the pressure issue. The new tank is very light, so it does seem to be working. But if anything, the pressure for the valve is even lower.
If I disconnect the pressure tank, the flow from the hose is pretty low.
I also tried turning up the water pressure from the source, which had no effect -- except on the pressure out the sink faucet.
There are no obvious kinks in the hoses. What's the best way to diagnose this?