My Take on a do it yourself pool heater made out of black tubing. Frame is two treated 2×4’s. Has 500′ of 1/2 inch black tubing. Splitter feeds 200′ and 300′ of tube in two different paths. I will feed it with 100′ of 3/4″ tubing from the pool.
FYI, when I had it leaning against the shed filling the pool it was probably taking the temp up about 10 degrees from the tap temp and flowing much faster than it will be when it’s getting pool water pumped through it.