Cause of low pH?

[Dave]

Sorry for this being long, but....

I'm having problems with low pH in my 4 foot tank. The pH began
dropping several months ago, to about 6.2 currently, and nothing I do
seems to bring it back up around 7 (my tap water), short of adding
bicarb every few days. However, I'd prefer not using chemicals if
possible. I searched the groups but can't find an answer.

The tank only has a small murray cod in it. Substrate is washed river
sand which I'm sure doesn't alter the pH (I sat some in distilled
water for a couple of weeks and noticed no pH change). Filtration is
below-the-tank trickle. I use the sump to keep live food for the cod
:-) I don't own any test kits other than pH, so I can't give water
parameters. Although my LFS said our tap water had 'medium hardness'
and shouldn't be a problem.

Huge water changes help, but within a couple of days the pH is low
again. The only chemical I add is chlorine remover. I put some crushed
coral in my sump several weeks ago, but this hasn't helped. The tank
is kept fairly clean. No pieces of food lying round and I stir the
gravel to remove detritus.

Could CO2 levels have something to do with it? If I do a test, and
leave the test water out overnight, the solution slowly turns back to
blue. However bubbling air through the solution to equilibrate it to
atmospheric levels quickly, no change in color occurs. If I bubble air
through my tap water, it remains blue.

So I'm puzzled. Something seems to dissipate from the water, either by
evaporation or reaction, but what? I thought at first it could be high
nitrate levels, but how can that be if huge water changes every day
don't fix it?

Hypothetically, if high nitrate/nitrite/ammonia, or low hardness was
not the problem, and there is nothing but substrate in the tank, what
else could cause a pH crash?

Dave

[NetMax]

"Dave" > wrote in message
...
> Sorry for this being long, but....
>
> I'm having problems with low pH in my 4 foot tank. The pH began
> dropping several months ago, to about 6.2 currently, and nothing I do
> seems to bring it back up around 7 (my tap water), short of adding
> bicarb every few days. However, I'd prefer not using chemicals if
> possible. I searched the groups but can't find an answer.

Starting with the basics, you would need to pour a glass of tap water and
measure the pH. Leave the glass on your counter for a day and repeat the
pH test. Any CO2 outgassing between the 2 samples would affect the pH.
The 2nd reading would be where your tank's pH settles, not the first.

Any meaningful analysis really needs to include the kH measurement of
your tap water and your tank water. This will speak volumes.

> The tank only has a small murray cod in it. Substrate is washed river
> sand which I'm sure doesn't alter the pH (I sat some in distilled
> water for a couple of weeks and noticed no pH change). Filtration is
> below-the-tank trickle. I use the sump to keep live food for the cod
> :-) I don't own any test kits other than pH, so I can't give water
> parameters. Although my LFS said our tap water had 'medium hardness'
> and shouldn't be a problem.

Clues: sump filter & live food storage.

> Huge water changes help, but within a couple of days the pH is low
> again. The only chemical I add is chlorine remover. I put some crushed
> coral in my sump several weeks ago, but this hasn't helped. The tank
> is kept fairly clean. No pieces of food lying round and I stir the
> gravel to remove detritus.

It sounds like your tap water is kH poor (under 3-4 degrees).

> Could CO2 levels have something to do with it? If I do a test, and
> leave the test water out overnight, the solution slowly turns back to
> blue. However bubbling air through the solution to equilibrate it to
> atmospheric levels quickly, no change in color occurs. If I bubble air
> through my tap water, it remains blue.

The reagents for the pH test are only accurate for a very short while.
The directions say to read immediately. Any subsequent colour changes
would probably be meaningless. If you are bubbling air through your
water sample, you will drive it to atmospheric CO2 levels (3-4ppm) more
quickly. Already noted above.

> So I'm puzzled. Something seems to dissipate from the water, either by
> evaporation or reaction, but what? I thought at first it could be high
> nitrate levels, but how can that be if huge water changes every day
> don't fix it?

What are your NH3/4, NO2 and NO3 readings? Get your LFS to write the
numbers on paper for you. Also kH and gH and get them to do the pH test
(not all pH tests are the same, there is ranges, accuracy and expiry of
reagents to consider). There are also some minerals which play havoc
with pH test accuracy (causing a colour which does not exist on the
colour chart).

> Hypothetically, if high nitrate/nitrite/ammonia, or low hardness was
> not the problem, and there is nothing but substrate in the tank, what
> else could cause a pH crash?

Anything which decays will lower your pH. This includes organic wastes
caught in your wet/dry filter, and ammonia from your fish (or your fish's
live food). Driftwood, plants (organic matter) will drop pH. The rate
of food being introduced into the system will give you an idea of what is
finding its way to the end of your food chain. If your wet/dry is
capturing this stuff and letting it dissolve into organic compounds, then
this will certainly put pressure on your kH and then your pH.

I hope there was some useful ideas in there.
NetMax

>
> Dave

[Mean_Chlorine]

Regarding the pH problems you guys seem to have...

DOUBLE CHECK YOUR PH TEST KITS! pH test kits have quite short
shelf-life, and more often than not, IME, they're off by a unit or
more. Try to measure a known pH, or ask your LFS to measure pH on a
sample of water from your aquarium.

If you find you really do have problems with low pH:

1) Limestone. Put limestone rocks, seashells, or chalk in the
aquarium, and it'll in a week or so raise the pH to 7.5, and stabilize
it there. For better effect, put crushed chalk in a bag in your
filter. However, the effect of limestone is slow and long-lasting, so
in extreme cases (e.g. heavily stocked goldfish ponds) it may not
dissolve sufficiently fast to replace the bicarb lost to filter
bacteria, and you may have to also add...

2) Sodium bicarbonate. This will instantly raise alkalinity of your
water, meaning it can neutralize more acid. Bicarb will drive pH
towards 8.3, and stabilize it there. Much faster and slightly more
dangerous than limestone, as it raises pH above 8, meaning ammmonium
in the water turns to ammonia. Don't raise pH with bicarbonate without
doing a large partial water change first, to minimize the risk of
ammonia poisoning. Otherwise bicarb is safe, and almost impossible to
overdose.

But always start with limestone of some form. Don't use dolomite or
marble, they dissolve too slowly to be of much use for maintaining pH.