Oily surface film

[matt]

Afternoon all,
I have an 100l open top tank which has suddenly developed an oily surface film overnight,
was fine yesterday.
It's lowtech and I'm not dosing EI,but recently(5 days ago)added KNO3 because my Limnobium laevigatum was looking very yellow and falling apart,would adding the KNO3 be the cause of this?
Thanks,
Matt.

 

[Fern]

Hi,
No idea about the cause, maybe someone more experienced than me might answer that, but I too had some issues with an oily film on the water surface on one of my tanks, so on a recommendation from this forum, bought an Eheim skim350, works a treat. I use it with a timer, for just a couple of hours a day, and not had any surface build up since using it.
Fern