Really simple solar hot water heater for Hot Tub

Simplest possible solar hot water heater to heat my old inflatable hot tub.
The pump is a mains powered 10W submersible pump costing £11. I tried a 3.5W solar panel powered pump but it wasn't powerful enough.
To do next: add another hose. Paint the hose and the wooden palette black.

[@stringbean1010]

where is the solar panel ?

[@AbbeyAerialVideo]

There isn't one. The sun heats the water in the pipe