I have a pool chlorinator for some years already, and recently the lcd screen has developed a brown line in the middle, like a burn mark.

I have seen similar symptoms on other lcd screens in the past, but that was mostly because they were exposed to sun or another heat source, which is not the case here.

The text on the screen starts to fade and become unreadable, and I have the impression that some days it is worse than others, but that may be just a false impression.

I assume that the lcd can be easily replaced as such a screens are standard and can be ordered from online component dealers.

The only thing I don't know is if my assumptions, that this is just a minor issue which happens all the time, are correct or that this may be a n indication of other more serious issues.

LCDs do wear out, and they lose contrast when it gets hot (so changes day to day are possible).

Whether it's standard one can't tell without taking it out, does it have special graphics?

LCDs do wear out, and they lose contrast when it gets hot (so changes day to day are possible).

Whether it's standard one can't tell without taking it out, does it have special graphics?

What you mean with special graphics?

As far as I'm aware it shows only text and digits and the usual symbols like %.

Do you mean, would have to remove it from the pcb to find out?

If it showed, say, a fixed image of a cloud (not relevant for a chlorinator but it's early) that would be special / custom graphics.

You'll need to pull the beast to find a part number to get you going in the right direction. The manufacturer of the unit would be a good starting point, it may be available as a spare.