Racking Carboys vs. FlexTanks

Over the weekend, I racked all of the 2013 wine off the lees in the carboys and the FlexTank.  The temperature in New York's Hudson Valley has been in the single digits and in some cases below zero on the Fahrenheit scale. On one of those cold days, the nozzle in the oil furnace that heats the winery became clogged and the furnace shut off.  Fortunately, I have a cold sensor with an alarm system, so a repair was made before any pipes could freeze. The one day temperature drop in the cellar resulted in significant precipitation of acid crystals along the inner walls of the FlexTank.  The polyethylene terephthalate ("PET") carboys showed less precipitation of tartaric crystals but showed significant yeast clearing.  My observation is that the wine appears slightly, but noticeably, darker in the FlexTank than in the carboys.  While I did my best to eliminate any headroom in the FlexTank, and I use a high density thick-walled tank, the FlexTank is breathable and oxygen may be affecting the wine even over short 1-2 month intervals.  The final results won't be available until I pour a glass from a finished bottle, but I am keenly watching any effects of oxygen on wine in the FlexTank.  I'd be very interested to acquire an eighty (80) gallon non-permeable PET tank, but so far it doesn't look like many companies make such a tank.  One company in Vietnam, Minh Hung, makes large 100 gallon-plus PET tanks, but since the risk of plastic decomposing and leaching into wine is significant, I'm still hesitant to buy direct from a vendor in Asia.  Below is a link to Minh Hung's site, which looks very professional:  http://minhhung.vn/en/minh-hung-pet-tanks.html.