My washer low indicator is permanently on even though the reservoir is full.

I’ve used Aldi winter washer fluid but reading on line I found that the system may be dependent on the MB fluid which has a different conductivity.

So can I cure the warning light by siphoning off some fluid and filling with genuine MB fluid ?

I had a similar issue on my VW after using Rain-X screenwash additive - Iregularly checked the level visually and just topped up with plain water (it was summer) and the warning eventually went off - subsequently I use either VW fluid or Prestone without any further issues.

Washer bottles usually have some sort of float which as it goes down triggers a sensor. I don't think the brand of fluid maters although cheap stuff can cause problems with the jets

I found that the system may be dependent on the MB fluid which has a different conductivity.

That sounds like a disgracefully sneaky way to make users buy special stuff when normal logic would say bog-standard screenwash should be more than adequate.