From: putzolu@toadflax.cs.ucdavis.edu (David Putzolu)
Newsgroups: alt.aquaria
Subject: Re: Troubles with undergravel filter
Date: 10 Nov 92 04:41:27 GMT
Organization: Department of Computer Science, University of California, Davis

In article <0ezNWib0Bwx24_90o_@transarc.com> Pat_Barron@transarc.com writes:
>Pardon if this is an FAQ - I'm new at this, and can't figure out
>what's going on.  Or, more accurately, I think I know what's going on,
>but I'm clueless as to how to stop it.

You should have looked under the "air-bubble geyser" heading - it
explains it all there. :>

>I have a 5.5 gal. aquarium with an undergravel filter and a small air
>pump (one of the smallest I could find).  Apparently, air builds up in
>the undergravel filter.  Every few minutes, kind of like a geyser, it
>spews forth all at once from one corner of the filter (it's always the
>same corner), producing a violent agitation of the water in the
>aquarium.  I'm concerned about what kind of effect this might have on
>the fish (though they seem to be getting used to it), and I also find
>it kind of annoying, since the "air-bubble geyser" makes a *lot* of
>noise when it goes off; I was considering putting the tank in my
>bedroom, but that's definitely not an option as long as this condition
>exists.

Sounds like the airstone (or whatever you have at the end of the
tubing going into your uplift tubes) is just too low. Something like
the following lovely ascii drawings...

What happens when stone is too low:     What happens when stone is just right:
       | o  H o  |                             |o  oHo   |
       |o   Ho o |                             |  o H  o |
       |  o H    |                             |o o H o  |
       |   oH   o|                             | o oH   o|
       |o   Ho   |                             |oo  Ho o |
       |   oH o  |                             |  o H   o|
       | o  H   o|                             |o  *** o |
       |  o H  o |                             | o*****o |
# ## # |o   H    | ### #  ## ### ##      ## # #| o*****o |## ### # # ## ### #
#######|o  *** o |#################      ######| o*****o |###################
#######| o*****oo|#################      ######| o*****  |###################
_______|oo*****oo|_________________      ______|         |___________________
    oooo o*****o   o  o
          *****o
___________________________________      ____________________________________

See, the bubbles can get caught under the UGF plate if they are released
into the tank at below the level of the plate. After awhile they will
build up until there is enough pressure to go through the substrate,
in effect a 'geyser' of air. By moving the stone up in the uplift tube
about half an inch (ok fine. 1.5 cm or so) you should be OK. 

>--Pat.
| David M. A. Putzolu               | putzolu@cs.ucdavis.edu               |
| Senior, CS & Psych, U.C. Davis    | op disclaimer(opinion : ptr mine)    |
| "Put your hand on the TV screen and repeat after me: I do hereby promise |
| only to watch the Ren & Stimpy show,  to make underleg noises during the |
| good scenes,  to wear unwashed lederhosen  every single day  of the rest |
| of my life! That's it! You are in our secret club!"                      |