If you can not measure it, you can not improve it.
To heat your pool efficiently with a fine designed solar pool heater, you will have to understand some things. It will take a little time but will help you stop losing time at bad design.
Here are the simple calculations you have to make to know the power you collect from the sun:
The formula is:
Qs = Ms x S x deltaT
Qs = Heat per second = Power (Watts)
Ms = Mass of water flowing per second (g/s)
S = Specific Heat of Water (4.186 J/g°C)
deltaT = Temperature change (°C) = output – input
Just by looking at the formula, you can see the power increase when water flow increase. So you need to seek the maximum water flow in your collector.
After that you can understand why the spiral hose design is not a good design, the water flow is too limited by tube length and diameter.
Now you just need to measure water flow (using a container of known volume + chronometer) and temperature input and output (with thermometer, not IR thermometer, a real one) and you will know the power of your solar pool heater.
If your collector is perpendicular to the sun, the light deliver 1000W/sqm on your collector a sunny day. You will find only a part (because loss) of this at the output of your collector (and then in your pool).
Never forget, the best way to learn is experiment by yourself. But no measure = no know.