White Foam on Surface After Vacuuming

I vacuumed my pool yesterday after having been away for the past five days. There was a whitish residue on the floor of the pool that was easily agitated with a brush, so I vacummed. I am pretty sure that the residue went straight through the filter and back into the pool, but I didn't feel like vacumming to waste. Anyway, as the water was coming back in through the returns, it was foaming on the surface. The foam was pretty thick, enough so that I repeatedly distrubed it in the skimmers as to continue to draw more foam in from the surface. The foam was gone within 45 minutes. I am at a loss as to what the foam could be. I have not used any algaecide in at least 3 weeks. At this point, I am only adding calcium hypo as shock and chlorox as chlorine, with the occasional supplement of trichlor tabs (to cover the long weekend when I was away). The foam is not there when the pump is running unless I vacuum. This happened once before, but I wrote it off as either algaecide or dead algae that the filter failed to catch, but that would not seem to be the case now.

These were the measurements I had at the time I vacummed. I have since adjusted my pH and FC.

FC - 2.0
CC - .2
pH - 7.2
TA - 110
CH - 350
CYA - 60



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33,000 gallon plaster pool
Jandy L-Series -CL580 Cartridge Filter

The foaming was probably the prior doses of algaecide being broken down by the chlorine.