Coolant disappeared from condensing tank

With the engine cool remove the cap - Is it full to the neck in the radiator? If so - that's good.
You could have had some bubbles in the lines which are still working out through the cooling system (recent coolant change?)

How much you are losing?... If it never needed filling it wouldn't need to be checked.
A very small amount can be normal. It can also be a very minor leak in a hard to see place.
There are many places hard to see, so not seeing anything obvious means only there is nothing obvious to see.
It doesn't mean there isn't a leak.
On a hot engine, coolant evaporates, which is why a dye is sometimes used to track down pesky leaks.

The car could also be burning coolant if there is a head gasket issue. Does your oil look good?

My oil as far as I see looks great.
The rad itself full every time I open it.
Also the upper turbo tank is full.
I didn't changed recently the coolant, I'm with mishi rad and stat, and it is winter here now ,could be cause the very low temps outside and the stat open very early.
I add half acup maybe ,no more than that.

Sent from...somewhere

Coolant is temperature sensitive, so if you noticed the change along with lower temps that could be part of it.
If it continues, you likely have a small leak that if you can't find is only a problem if you run out of coolant.
If it gets worse, you will likely more easily be able to find the leak...

My old LGT would always drop below the low mark and stay there. Haven't peeked at the 2017 Forester other than seeing there is coolant in the overflow tank. My guess the level will stabilize.

Well...when I say the level drop i mean that it's going down the max mark not the min, idon't know why but I like to see the level at the max mark, something with my brain is wrong... i guess

Sent from...somewhere