Solar Pool heaters

Hello,
I’m new to the forum and I”m looking for some opinions on solar pool heating. I live in the North East (NJ) and my pool is 20’ x 40’. I’m looking for a solution for heating my pool. Currently I have a 400,000 BTU gas fired heater and I use a solar blanket at night. I’d like to find a more economical solution instead of the heater. I was looking at an evacuated tube solar system but no one will tell me the net gains the system can produce. I understand it’s based on the hours of direct sunlight, but I’m just looking for an average in my area of the country. Can I see a net gain of 10 degrees, 15 degrees?
Does anyone have a system like this, if not what are you using, what kind of gains are you averaging and are you happy with the system
Thanks everyone