Looking to ID Algae in Sump

[CHEAPREEF]

So it's been 2 weeks and no return of the white slime or the buildup in the pipes. I can't be 100% what it was yet but I am leaning towards a build up of VOC's in the water.
I am going to start adding stuff I stopped doing slowly every 4-5 days see if anything triggers a return, other than the AA's and Bacteria I no longer feel the need to dose those as the tank has been perfectly fine without either.