It sounds like you have a pressure side leak. Some where under the ground after your filter. If your filter was leaking the amount of water your pool is loosing the pad would be flooded.

Some things to check.

Leaking out of the backwash
Leaking from hydrostatic valve in the main drain
Leaking through the back of the light niche
Leaking in the skimmer mouth or skimmer

But since your pool leaks more when on means you have a pressure side leak.

Hope this helps