C.pygmaeus cant come down to the bottom!

[unotim123]

1. Water parameters
a) 24 C
b) pH.(I dont know now but a few months ago it was 6.8 and my water parameters dont change frequently)
c) GH.10
d) KH ?
e)Ammonia=0 Nitrate=10 Nitrite=0
f) Water change frequency=once in two-four weeks


2. Tank set up
a) Size=30 lt
b) Substrate=0.3-0.5 mm quartz and jbl aquabasis
c) Filtration=A sponge filter
d) Furnishings.
e) Other tank mates=Penguen tetra and black neons,C.rabauti and Ancistrus sp.
f) How long has it been set-up=Around 1 years.

3. Symptoms / Problem description

My C.pygmaeus cant come down to the bottom around 4-5 days.She try to remain at bottom but her tail rise to the water surface automatically.Then she hang water surface.I cant understand this situation.This situation occured with C.paleatus for a few times but rarely.

5. Medications used (if any)

I use Seachem prime for every water change.

Here is my aquarium photo.
http://img193.imageshack.us/img193/3522/pygj.jpg

[unotim123]

Fish dead.