I'm sure that's true, but the cause doesn't matter. Snails don't like pHs that
low, regardless of the cause.

I will try to encourage my girlfriend to add a little sodium
bicarbonate (each water change - and it's her tank, not mine), to
raise the kH to proper levels of at least 3. If I can convince her it
is a good idea I will add some oyster shells (first I have to obtain
them as I don't have any, but nonetheless) to also help with the
problem.

If that's the case, then I'd say the low pH is definitely due to too much
decaying organic matter in the tank. The biological process that creates
nitrate eats up the KH in the tank, and causes the pH to drop. It might help
to vacuum the gravel thoroughly.

I would tend to agree. During water changes the gravel is vacuumed
throughly and the filters rinshed/changed throughly (there is an Eheim
2080 and an Emperor 400) running on the tank.

With most KH test kits, you count the drops you add to a vial of water until it
turns color, and the number of drops = degrees. If you put in one drop and it
turns, the charts tell you that's 1 degree. But realistically, you can't tell
if your actual KH is 0, 1/2, or 1. All those KHs will result in a test that
turns color after one drop.

I used the Tetra kH test kit which allows you to use 10ml instead of
5ml if you want. So I know it is accurate at least down to 1/2 a
degree, other than that I don't have any other measure of accuracy in
that test. I suppose If necessary I can try using 20ml and seeing if I
can find a more accurate measurement that way, but using 10ml and
using the drops seemed fairly accurate compared to only using 5ml and
each drop equaling 1 degree.

pH and KH have a predictable relationship (shown on the pH-KH charts used to
detemine CO2 levels). There's one here on Chuck's page:

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

In a non-injected tank, the CO2 levels are 3-4 ppm. Knowing this, you can use
the chart and your pH values to figure out your "real" KH. With a pH of 6.6,
the KH is 0.5 or less. With a pH of 6.8, the KH is likely between 0.5 and 1.

The fact that your substrate is neutral has nothing to do with it. As you
yourself note, natural biological processes can lower your pH and KH. In fact,
it's normal for the pH and KH of a tank to drop over time, until you replenish
the KH with a water change.

Perhaps I'll start adding some sodium bicarbonate to the 55 to
increase the kH to increase those readings. What is a suggested
starting dose to slowly increase the kH at each water change?

If you add CaMgCO3 as discussed in the "oyster shells" thread, that will raise
your KH. The best way might be to mix it with water and add a measured amount
each day. The KH jumps up anyway with each water change, so adding it only
after a water change doesn't really make sense. That's when it isn't needed.

So, you suggested oyster shells rather than sodium bicarbonate? Maybe
I'm getting my terms fixed up - it happens often. I thought you could
add baking soda to raise the kH, am I just remember things wrong? I
know that you can add egg shells, oyster shells, etc. to raise the kH
and I may take that approach if I'm remembering wrong about sodium
bicarbonate.

You can measure your KH to get an idea of how much you're adding. If the KH
doesn't budge for a week, then you can up the dosage. If it starts rising too
fast, lower it.

Yeah, if I modify those tanks, it will be something I'll start to have
to definately measure each week or more to make sure the levels are
acceptable.

Are those readings you posted without CO2 injection, then? If so, something's
wrong. With a KH of 4, your pH should be 7.4-7.6, not 6.9.

Yes, those readings are w/o C02 injection. The pH test kit is the Red
Sea low range one recommended by Tom Barr. I don't know what would
explain the disparity in the pH readings of what it says it is and
what it should be according to that chart. I vacuum the surface of the
sand througholy making sure I get all the organic waste. There is a
filter attachement to the end of the intake of the Eheim 2026 that I
rinse every week that gets rid of a lot of organic waste. I just
recently cleaned the filter 2 weeks ago. So... I don't know where the
problem lies with this discrepency in pH. Any ideas?

You love apple snails but never liked mystery snails? Apple snails and mystery
snails are the same thing. Those are both common names for largish snails from
the Ampullariidae family.

I probably just didn't know the difference. I worked in a petstore
(unnamed at this time) and all I remember is that the mystery snails
had a penchant for eating anything organic which is why I don't like
them now. That page will better inform me as to which snails are good
for plants and which snails aren't. Sorry for harboring past
stereotypes.

I've always liked those very large apple snails that grow the size of
a tennis ball or so, but I've heard they are notorous for eating plant
matter. I will do futher research on Pomacea bridgesii and see if
their looks and eating habits coincide well with what I am looking for
- they aren't quite the size I was wishing for, but a litte variety
and extra help in the tank is appreciated. Thanks for the helpful page
on snails, it will come in handy.

I dislike invertebrates (they cost a great deal of money to purchase
here, the amano ones at least), but perhaps in the future I will look
into a pair or trio or even a group of wood shrim (still expensive,
but I like their look much more).

The further this discussion goes, the odder my tanks seem. I suppose
it's good I'm learning something, but it is sometimes crushing to know
that somewhere along the line things aren't quite where they should
be.