Wow! Even I'm surprised that it is THAT low.

Thanks for posting that.

Keep in mind that you'll need to reduce the backwash flow, or it will happen again. The fastest short term solution is a valve on the discharge line, allowing you to throttle flow.

Long term, a smaller pump OR a smaller impeller in the existing pump -- assuming you can find the parts -- will not only save your sand, but will improve filtration. Excess flow not only causes sand loss during backwash, it also causes dirt to be driven THROUGH the sand bed, and back into the pool!

Good luck!