air bubbles, low pressure...can't vacuum..hlp pls!!!

[fabchef]

Hi folks fabs here. I've been having problems with our pool now quite some time now. It seems that there are always some bubbles/air pockets visible in the filter cover.

info: we have a aprox: 80 000LT inground pool. Sta-rite filter and pump.
About 2 years ago we found a leak on the return line of the skimmer, we cut out the section and put in a new small section.

I don't know if this makes a difference, but, we've been at this house for about 5-6 years and we've never chnaged the sand in the filter and don't know when the previous owner changed it before....
the pressure on the filter is at 12psi. I asked a pool guy and he said it should be around 20psi!!! (i do my backwashes once a week, rinse too)

Whenever i close the bottom drain and attach either the automatic pol vac or if i do it manually....The pump takes in air and can't fill up with water, hence no pressure when vacuming...
Any advice would be great.

I have a gut feeling that there may be another leak in the skimmer return line, i don't wanna have to dig it up, but if i gotta, i gotta....

[jdmadda]

I have all these problems plus one of my returns has very low pressure and I have air in the other return. Same deal with the sand, hasn't been changed in at least 5 years.