We have a Doughboy 21 ft round above ground pool. I bought the Intex Krystal Clear Sand Filter Pump for above ground pools, 2800GPHPump Flow Rate and the first two times I vacuumed it worked just fine but then I started losing water in the secondary filter basket ONLY when vacuuming after a few seconds. I contacted local pool companies and they said was likely a air leak in hose cause by pinhole so bought a new hose-Nope-still does it. IF I take the hose out of the hole connecting under the skimmer basket but hold the flap down to let water continue to flow with the skimmer lid down for vacuum function-the secondary basket does not lose water so it has to somehow be related to the hose and the water flow rate but for the life of me I can't figure out what it is.