We have a brand new in-ground pool and hot-tub. Big pool- 50x20, big spa, 10x9. We have a big heater too- 400 btu propane heater. However, even when the starting temp of the spa is 81 or so, it's taking over 1.5 hours to get up to 99-100 degrees! I think that's WAY too long. We worked with a...