It is NOT the same as Borax. D.E. (Diatomaceous earth) powder is the filter media used in D.E. filters. It can actually filter out smaller stuff than a sand filter. Many of us with sand filters add a little to help it filter out the small stuff. You can read more info about it in the following thread:

http://www.poolforum.com/pf2/showthread.php?t=3742

When will you be home? It would help to know if you are losing more than 1ppm of chlorine from sundown to sunup the next day. We recommend that people keep a high cl level until they aren't losing more than 1ppm of cl overnight.

How does the water look?