Air in sand filter

When using any restriction at the skimmer eg connecting a pool cleaner, I get considerable quantities of air passing through the system. This indicates a leak on the suction line. Additionally, the filter does not work very well. I believe dirty water is getting back into the pool in this condition. My question is: would one expect the air to create sand conditions which would allow dirty water to get through?
Without any air apparent in the system, the filter seems to work although I have not yet achieved a clean pool yet because of the above.

Air flowing through a sand filter will tend to 'mobilize' the dirt; this is used sometimes to help clean (backwash) large commercial filters.

Can't say if this is contributing factor in your case. Again the DE test will tell: add a couple of cups of DE to your skimmers with the pump on. If DE shoots back into the pool via the pool return . . . your filter needs repairs.

Ben