Hi del....
I just thought you might want to know,
You can leave a hydro system alone for very long periods 7-14 days(more if need be)
You will have a back up resivor that drains into your "regular" resivoir.

This back up is PH and PPM perrrrrrrrfect... it is a simple thing to do... it runs off of gravity ... a gravity switch... most hydro stores will sel you the parts...
Any hydro system can be adapted to use an extra resivoir..

: )
smb