Pet Forum / Aquaria / Cichlids / November 2005

Hi!  I think changing the gravel will stress the fish.  What I don't
know is what the consequences will be.  They may just be a little
stressed until you're finished and will return to normal when you're
done.
Why do you need to change the gravel?  How long has the old gravel been
in the tank?  There is the problem of destroying the bacteria on the
gravel with the resultant ammonia/nitrite spikes, which could really
stress the fish.  Is the tank lightly or heavily stocked?  What kind of
filtration is employed?  How long has the tank been set up?
Sorry for all the questions, but they are just some of the things I
would consider before changing the gravel
Bob C.

Yes.  The procedure is to remove the rocks from one half of the tank.
Then siphon out the gravel from that side, getting as close to the
remaining rockwork as possible.  I would not remove the gravel by any
other means (ie: scooping) as it will release too much debris into the
water column.  For siphoning, you should use a larger diameter hose (I
use 2"), and depending on your gravel weight & depth (determines the
total weight to move) and the lowest end of the siphon (determines vacuum
pressure), you might find that it takes several days to do a bit at a
time (unless your fish are accustomed to large water changes, as it might
take 10 gallons of water to move 5lb of gravel).  This will vary
tremendously according to your specific conditions though.

If the fish are accustomed to large water changes, then stick a hose of
incoming temperature adjusted water on the opposite side, overdose with
de-chlor and you should be able to siphon half the gravel in one go (and
a bit of patience).  We would siphon gravel down into styrofoam coolers
and have a Python continuously sucking the water out, leaving (mostly)
only the gravel, but the siphon would go faster than the Python or the
return water filling the tank, so you pause occasionally to let the
levels catch up.  Check your incoming water temperature periodically
(it's a bitch when it goes cold on you, and you took too long to notice).

With fish inside, I would not do more than 1/2 the tank at a time, and
leave your filters undisturbed.  The most important nitrifying aerobic
bacteria are mostly in your filter, but the gravel also has some
anaerobic bacterial cultures which break down detritus and other organic
matter.  The filter bacteria are the most critical as their reproduction
rate is quite slow (almost a day), but the gravel bacteria is from my
understanding, the much more conventional species which double in the
typical 20 minutes, so they are less of a concern.  Allow a week to go
by, monitoring water quality (NH3 & NO2) and if all is well, move the
remaining rockwork to the empty side (use a plastic putty knife to shovel
over the gravel the cichlids have blown to the clear side), and then
siphon the rest of the gravel.

It is a little tricky putting new (or clean old) gravel into an existing
tank without getting a lot of fines (gravel dust) into the water column.
For this, get the large siphon hose and install a funnel.  Now pour the
gravel through the funnel when the other end of the hose is touching the
base of the aquarium.  This will minimize the cloudy water somewhat, but
expect it to still take a few days to clear properly (if you haven't
cleaned or replaced your filter media, and it is nice and sticky).

When all is said & done, the above procedure works even better and faster
if there are no fish in the tank, but it's up to you to decide what best
fits your application.  hth