I have a acrylic spillover spa that shares the pool pump & filter. After about 30-40 minutes of use the hot tub starts to lose prime. At the same time the hot tub is losing prime I can hear gergaling noises coming from the pcv "U" "J" vent traps installed above ground behind the spa/pool. It sounds like air is being sucked in throw those PCV pipes? This also seems to happen when the heater is on....
Any ideas what the problem could be and how to fix it???