Low-budget automatic doser

I've read this stuff about I.V. dosers for administering PMDD's (or
whatever).  One problem with I.V.'s is that the bag needs to be kept
above the tank, and having such a bag can be rather unsightly, and
it'd be hard to keep your bag in the dark (so that the iron doesn't

Lately, I've considered building an electronic doser.  The basic plan
is to hook up a 9v DC power supply (cut off other doo-dad), and supply
that from my light input (which is timed to turn on once a day.)
I figure to build a circuit out based on a 555 (timer) chip that,
immediately after being turned on, will, for a few of seconds, power
a relay that controls power to an old air pump.  The output of the air
pump will go into a bottle of PMDD's, which has another air-line
that leads from the bottom of the bottle into the aquarium.
(Of course the bottle is sealed, aside from the two air-line tubes,
so that air from the pump forces liquid into the tank.)

The whole aparatus should be very low-power, small, cheap, and discretely
hidden under the aquarium.   I haven't had the chance to try this plan
out yet 'cause I loaned my bag-o-electronic-doo-dads to a friend.
Anybody have any wisdom to share on the subject?

                                        - Steve
Steve Benz (steveb at tall-tree_com)   |   Tall Tree Software Co.
http://www.tall-tree.com            |   Ph/Fax: 512-453-4909