First, I will answer your specific question. The WhisperFlo WFE-28 is a very high performance pump. It can do very high flow rates at lower head, and it can generate high pressure (up to about 37 psi).
It will do 120 gpm at 40 feet of head and about 45 gpm at 85 feet of head.
My opinion is that you should have about 1 square foot of filter surface area for every 15 to 20 gpm of flow at the lower end of the head curve (low resistance, high flow).
120/15 = 8 square feet. 120/20 = 6 square feet. The average is about 7 square feet.
The Triton II TR-140 has 7.06 square feet of sand surface area.
If you’re going to keep your existing pump, I would recommend the TR140.
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Now, the question is do you really need such a big pump?
My opinion is that you almost definitely do not need such a big pump. Unless there is a reason you need such high flow, you would probably be better off getting a much smaller pump or a variable speed pump.
If it’s an old pump and your electrical rates are high, I think that it’s an easy answer, replace the pump.
It it’s a newer pump and your electrical rates are low, then it’s much harder to justify replacing the pump.
How old is the pump and what are your electrical rates?
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The next question is do you really need a new filter? A DE filter works quite well as long as it’s sized, operated and maintained properly.
Which specific filter do you have and how old is it?