I wouldn't recommend leaving a male/female pair together all the time either. Over breeding and constant egg production takes its toll on the female unless you intend to cool them both for a few months to stop egg production. Year around egg laying can greatly increase a calcium crash.

Two females of nearly equal size can do well together all the time though I would provide separate feed dishes to limit competition for food and make sure there are plenty of plant cover, either artificial or live or combination of both. Visual barriers help avoid stress and competition.

For now, definitely continue to keep them separate till the smaller one catches up in size and you are certain of its sex.
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PHLdyPayne