did you ever get around to testing for nitrates, etc? I also think your grow-out tank was too heavily stocked/under filtered/too small of a tank to handle the waste. especially if you are over feeding to get growth.
I mean I over feed and rite after like 2min after food is gone I do a wc ...NEVER overfeed, its the number 1 cause old death for beginners! The over feed could have caused an ammonia spike in the small tank
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