Hello Jonathan, I see that you have used DesignBuilder to develop the model and add the swimming pool afterwards. I have done this before with realistic results, but as you can see in the bug I reported (https://github.com/NREL/EnergyPlus/issues/4805) water flow input was asked in m3/s while it actually was used internally as kg/s.
It seems to be corrected in v8.4 but there may be still a bug there. It seems that they have not updated Energy+.idd file and still shows m3/s as unit in the IDFEditor. I will report that in Github.
Hope this clue is useful for you...
Cheers,
Germán.