I’ve done root pruning in the past when I had them in 1/2gal square containers, but with these little ones I’m just starting new moms.
Standard over the counter 3%, I mix 1:1 with water, and flush with it till run off or even sit it in a tub to let it soak too. Do that and let it drain the dry before watering again. If your using organic ferts, you might want to reintroduce more good bacteria too