My 175w MetalArc lamp tends to take very long to start the arc. Why does it also appear to me that the probe has been buried in the (halide) salts?

What is the position of your lamp in the fixture?
It is the lowest point when cooling down, so the condensed salts flow there.
Or it is the coldest point during the lamp cool down, so they even condensed there.

The long time to start up may be linked to the probe buried in the salts...

So try to change the lamp position...

What is the position of your lamp in the fixture?
It is the lowest point when cooling down, so the condensed salts flow there.
Or it is the coldest point during the lamp cool down, so they even condensed there.

The long time to start up may be linked to the probe buried in the salts...

So try to change the lamp position...

It was used in a diagonal/vertical position.