Water Film in Return Compartment

[martinmcnally]

I noticed a few days ago if I disturb the film that builds up on top of the water in my return section of the sump that the SPS corals do not like it at all. All polips close up for a few hours. Wondering if I may have gotten some kind of oily pollutant in there or is that normal? Today during water change I sucked it all out but the SPS still not happy with me touching it. Anyone else experienced the same?

When I was sucking out the water in there today I did see some kind of slightly different colour fluid on top of the water.