I am a returnee to the planted aquarium world after a long hiatus--in
1989 an inconvenient earthquake destroyed all my tanks (plus my house)
and I am now at long last setting up a new tank. But a strange thing
is happening. My tank water is testing alkaline off the chart--my test
kit only goes to 7.8. So the pH is at least this.
My tap water is from a well. It has a lot of iron and manganese
in it. It tests at 7.0, with 8 dKH. I softened my aquarium water to
6dKH with distilled water. My old time tanks, same well water, were
heavily softened with rain water (it does not happen to be raining at
present), and were always mildly acidic, as one would expect.
I can only figure that I put some wildly alkaline object in my
tank. But what could it be? This is what is in the
1. a half inch of terracotta pottery clay covered by
2. an inch to 3 inches mixed garden loam and vermiculite. This garden
loam has grown vegetables and flowers for years, and I have no reason
to believe it is anything but ordinary clayish loam. I have not tested
it, however.
3. topped by about an inch of mixed masonry sand and used standard
aquarium gravel
4. driftwood, and granite and sandstone rocks from my local creek all
of which I used for years in the past without problems.
5. slate siliconed to the glass for terraces.
6. plants, in variety. No fish yet, and I don't dare put any in, with
this water.
7. DIY CO2 teed into the intake of a Eheim cannister. I haven't done
this before and the CO2 seems to come through in a glob every few
minutes, causing the filter to hiss and gurgle.

It is a 29 gallon tank with a 55x2 watt bright kit from AH Supply. My
scientist husband suggests adding something acid to the water to get
neutral pH and see what happens next. I know there are such additives
sold for aquarium use, but is there something safe to add from around
the house? Peat seems like it would be too complex an acid and would
make it hard to interpret what was happening.

Any suggestions gratefully received.

KMS from central California