Cory's sensitive to 4 year olds...

Hi,

I've got a male betta and two tiny cory's (corydoras pygmaeus I think
....photo at http:\\www.muddylittletaoist.org.uk\pigmycory2.jpg ) in a
22 litre tank. They have previously been very happy little guys
playing in the bubbles and scooting round checking out everywhere for
food but more recently they've started spending much more time just
sitting on the gravel and are quite skittish when anyone comes near the
tank. I've tried watching them after lights out but they seem the
same. The only time they seem busy is if I come into the room when
no-one's been there for a while and then they seem more normal. They
still play from time to time and have no signs of illness that I can
see but this has been going on for a few days now and I'm getting
concerned.

In terms of tank conditions we've got:

NH4 = 0ppm
NO2 = 0ppm
NO3 = 10 ppm and 25 ppm
Ph = 8.0
Temperature = 25 deg C or 77 deg F

I do a 25% waterchange weekly or biweekly depending on NO3 levels at
weekly test.

I'm feeding flake mainly with bloodworm and brineshrimp treats.

There are three things which might have caused this problem that I can
see. One is that I noticed that the corys seemed to be getting
precious little in the way of food because my betta will practically
take it all from my hand. So I got some catfish pellets and have been
putting 2 of those in every other day to top them up. I guess it's
possible that they're less active because they're just not hungry
anymore, so if I slow down with the pellets they may become more active
again?

The other thing is that my 4 year old ran his remote control car into
the side of the cabinet the fish tank sit's on. It made an almightly
thump and resulted in him getting banned from playing remote control
cars near the tank. It's really since then that the cory's have been
skittish. I think it scared them stupid at the time. Perhaps they are
sensitive, especially with fewer pals around they they might want and
take a long time to regain trust in their environment. The tank is
heavily planted and so does provide lots of little hiding places which
they use when they feel less safe.

The only other thing is that I changed one of my plants recently
because it wasn't doing too well in the lighting I have in this tank.
This disturbed the substrate allowing some of the mess from my
undergravel fertiliser balls to come up. I did a 30% water change
after just to be sure, the tank looked clear after that and the water
parameters didn't shift noticably. The fertilizer is nothing special
just trace elements and iron.

I was thinking that I might be able to fit another cory in this little
tank without pushing the stocking levels too much and I wondered if
that might help because I know cory's like to school and these pygmy
chaps like to school in their thousands in the wild.

Ho hum,

Anyone got an ideas?

Thanks!

muddy