Ph Probe Remedies

First of all I would like to say thanks for all those people who offered
advice on how to fix my Ph probe problems.

Over the weekend I started playing around to see if I could resolve the
problem. Things got worse before they got better. I discovered that if I
turned my heaters off I would also get a variance in my Ph reading. I first
tried covering the emersed portion of the probe in tin alfoil, but this had
little to no effect. Secondly I used a tin can in the same fashion as the
alfoil but this time I earthed the tin. I still had no luck. Finally I
decided to try earthing out the water and BINGO, all interference was gone.
I can now switch anything on or off without making any difference to the Ph
probes' reading.

The question I have now is what metal is safe to use in an aquarium?
Currently I have a piece of tin foil hanging in the water which is connected
to a piece of copper wire (thats on the emmersed section). I have contacted
the aquarium shop trying to locate a grounding probe but they told me that
they cant get them and if they could they would cost around the Aus $75.00
mark. Any suggestions would be welcomed.

IN drizzly cold Adleaide, South Australia. (Neon rainbows are now down to
around the $15.00 dollar mark). Oh, and for those interested in Aust
Natives, I hear that it will soon be illegal to collect Desert Gobies from
Coward springs (these have the best colours I have seen).