Swim Spa solar heater

Fiddling with 2 off uninsulated matte black domestic flat radiator panels heating a 7,000 litre swim spa. WEMOS D1 running DS18B20 1-wire sensors switching on a small pump when solar output exceeds spa temperature by 1 deg C. Total area 1.2 sq M, 700W
  thermal, solar, spa, heating, tub, jacuzzi, ds18b20, esp8266

Field 3 Chart
Spa water temperature
Field 1 Chart
Solar panel output temperature
Field 2 Chart
Solar panel input temperature
Field 4 Chart
Ambient temperature
Field 5 Chart
Pump status
Channel Location