Questons about culturing rotifers and phytoplankton

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I am thinking of culturing rotifers, I have read a fair bit about it, I have some questions about people's practical experiences doing this.

It seems there is a choice between culturing the phytoplankton (nannochloropsis) to feed to the rotifers, or using an "instant algae" type product to feed the rotifers. Which method do people find more successful?

I am also wondering about rotifer crashes, or phytoplankton crashes if I am culturing phytoplankton too. Is there a good way to have insurance against crashes, besides keeping several cultures going at once? Would rotifers or phyto survive either freezing, or being kept for long periods at near-freezing temperatures? Or is there another way to keep resting cultures of phyto or rotifers in case of a crash?

It is difficult for me to get starter cultures, so the issue of crashes is critical for me, with no one local to replenish my cultures if they crash.