I am somewhat new to pool ownership we bought the house 2 years ago with IG guinite pool. It is about 15 year old pool. I recently installed new Hayward VS pump. Recently I started noticing small bubble out of several of the returns ( we have 4 in the spa and 2 at shallow end of the pool). No SWG. The funny part which I can't figure out is that there are small bubbles only at high speed 3400 but at 1500 no bubbles at all. I already resealed the plugs and O ring for pump lid and inlet. We tried to use water over the different valves on suction side but bubbles persist. Any idea of what can cause bubbles only at high speed. Btw no bubbles at the pump that I can see but air does enter the filter especially when I have to start pump. It primes fine in about 1 minute. I don't see vortex at the skimmer although it does suck in water pretty well. The pressure is about 15 psi. Once air is drained from the DE filter via valve it doesn't reaccumulate unless pumps speed is charged.
Thanks in advance for all the help.