2 out of 3 houseplants have got white substance on top of soil..what is it?

[MilkshakeMaker]

And how do I fix it??

TIA

Mine occasionally get this too. I think it's some sort of fungus/mildew type of thing.

It seems to happen when the top layer of soil is wet, so I find that watering from the bottom helps. I ignore my houseplants for several weeks, then think "Oh, s**t" and soak the posts in lukewarm water for several hours to re-wet them.

This is probably completely wrong - but my plants seem to like it

Hi sorry about the late reply, has that stopped the top going white? I've had the plant since January and I'm so pleased it not dead, its flowering lovely so I'm doing well, its just that top bit, will try your tip! Thank you!