Pool vaccuming and low filter pressure?

[summer211]

Hi everyone. I am looking for advice. We are new home owners and have a pool that has the DE filter. First we were having problems with the pressure when the filter was on but we had someone clean the entire inside of the filter and we backwased it and it worked fine...

Now weeks later, we the filter seems to be working fine on its own. However, when we hook the vaccum up the filter pressure goes to zero or just above zero. Its strange because the hose is suctioning on to the basket but the filter makes a strange noise once you hook the vaccum in and then the pressure drops down to zero and no dirt come up at all.

Any advice? Thank