So I used to get unexplained crashes when I ran my phytofarm indoors under artificial lights. Not often, but it would still happened. Getting religious about sterilisation of the bottles only seemed to partially make a difference; I was never really convinced it improved it that much. When I went from 5000K CFL's to 6000K LEDs, I noted it did seem to also lesson the frequency of crashing.
Then, by chance, I learned about something and decided to do things fundamentally differently.
I now grow my Nannochloropsis the same way the Dutch farmers do it for the American Healthfood market - outdoors under natural sunlight. About the only difference is, where they have giant pools in the ground for this in greenhouses, I still use my 1.5L recycled Dr. Pepper bottles. But after that switch to sunlight, all my crashes stopped. I used to be very strict about bleaching my bottles, now I just hit them with 60C+ hot water and vinegar and a bottle scrub brush, and they're good.
Further, I've checked even with a microscope; there's been no contamination or supplementation by some other algaes; it's still Nanno, and we're rolling over onto year 5 this summer I've been going at it this way and not a single crash since moving outside under natural sunlight.
The bottles sit in a saddle like recycled toolbox with a handle in the middle. I use T-5 reflectors set on top of the bottles to keep rainwater from getting inside the bottle tops (I drilled holes in the caps for the ridged air pipette, but rainwater could still seep in through that hole, since it's not air-tight). One of the bottles has a digital temp probe that links to my aquarium controller, so I can monitor for freezing temp conditions (-1.5C). The recycled toolcase makes it easy to quickly and temporarily relocate the whole farm indoors for those rare winter days it get's that cold here.
