Thanks Mark, something to pay a bit more attention to with the dye in the water. I did have some flow figures somewhere and there was also a slight reduction in the flow with the smaller orifice but that due to only a tiny amount of energy being used at the pump, icing on the cake really but good to examine.

By way of comparison, the other larger pool I mentioned runs at 125 watts, 1400 RPM moving 63 US GPM, 0.5 PSI on tank gauge. When needed ( to pass regulation) we can crank that to 100 US GPM, 464 watts 2150 RPM, gauge reading 2.7 PSI but the pump could do more, sadly the builders fitted 3 skimmers but on to one pipe so the max we can draw is 100 GPM. That is a standard setup but the M/D is plumbed on a 3 port to do inlet and outlet for heating or cleaning if required.