I had a very similar situation a few years back. I could not keep my pH nor
my KH at any decent range dispite that my tanks were not even moderately
stocked or overfed. However, my live plants (mainly a large Amazon Sword
and a few Vals) would sprout like crazy after every water change and kept a
good growth pattern up. After some serious investigating, the best culprit
was biogenetic decalcification. Basically, what some plants do is strip the
water column of calcium buffers if they don't receive enough through their
normal processes. The result is a dropping KH and a low pH.

I solved this problem by adding a small amount of crushed coral to the
sunbstrate. Just dumped about a 1/4 cup in the tank and checked the KH and
pH levels. The plants may still remove the nutrients from the water column,
but the lower pH would disolve the crushed coral and there for replace the
buffers in the water. After a week of monitoring, if the 1/4 cup wasn't
enough, I added a little more. This way the water parameters are changed
slowly over time, just as the fish are used to, rather than shocking them
with a large change at once.

So far, I have not had any problems with KH or pH. I have had to
periodically add more crushed coral as time went by. Regular monitoring
will let you know when the last batch of coral is near it's end.

Justin

"chris nuttall" wrote in message
om...
hello everyone,
i have a puzzle.

in my 15 gallon aquarium, which is about 3 years old, i have;
breeding pair ancistrus (5" long)and their offspring usually twenty
ish tiny ones which go to the lfs at about 1" long,
2 siamese alae eaters / siamese flying foxes (4" long),
2 upside down catfish (2" long),
7 harlequins (1" long),
2 neon tetras (1" long),
1 whiptail catfish (4" long)
1 pygmy puffer (1" long)
1 large amazon sword plant and an abundance of reedy plants which i
occasionally pull out to keep them under control.


I used to have 3 pygmy puffers, but about six months ago 2 of them
died in the night. I checked the water and found the ph at 6.2 and the
kh at 4 degrees.
I did a partial water change only to find that the ph and kh dropped
agian over the next few days.
Since then i have been doing 40% water changes every week to stop the
ph dropping to a dangerous level. I have done a fair bit of reading
about ph and kh, and i understand ( from a fish keepers point of view)
the relationship between them.
At about the same time as the ph kh dropping started i noticed snails
in the gravel, their numbers grew rapidly to a few hundred ( i guess)
and are now stable.

The only process i know of that will cause kh to drop and then the ph
to drop is the production of an acid, and i think the acid must be
nitric acid produced from the nitrates present in the water.
The puzzle is this.
Are the snails causing too much bio load on the system?
Am i over stocked?
Am i over feeding?
or is there another possible cause for this drop?

I feed once a day an hour or two before lights out; 1 very small pinch
of flake food, one eighth of a lump of frozen glassworm (really only
for the puffer, but they all eat it)one algae wafer and one carnivore
wafer (the wafers are sometimes substituted with courgette (zuchini)

Sorry to ramble on but i see so many posts where the information
needed is not provided.

tank parametes after a weekly waterchange: Ph 7. Kh 9. nitrates 90ppm.
nitrites 0.

just before a water change the nitrates and nitrites remain the same
but the kh has fallen to 4 and the ph is 6.2 - 6.8.

any help gratefully received

chris nuttall