I only change pots when they're already distressed (bad mix etc) or when the roots are at the bottom of that pot. All the ones I moved to buckets had the root already at the bottom of the 100mm seedling pot and were on the verge of being root bound.
I had to pull and discard about 15 plants yesterday
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I've changed the soil mix to just budget potting soil, a lot of perlite and no nutrients included so I can control what nutes they are getting. Didn't use any coir-peat because retaining moisture is the problem at the moment. When it gets really hot, and if the soil is repelling water I might use a soil wetter. The roots of the new ones had filled their pots and I had to tease them out a bit so I'm confident they will fare better.
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