It is abosolutely awesome that they are recovering. I can't tell you how happy and thankful I am to hear that.
I don't think they will be more susceptible just because they've had it, but I would just strive to keep their environment as stress free as possible, their water pristine, a good variety of food to provide all their nutritional needs, you might even look into vitamin supplementation for them, and stay watchful.
I think once they fully recover, you don't need to worry too much.
How long did you go with the Maracyns, after you realised the correct dosing?
I think 10 days of treatment, at the full strength that is assured by the fresh mixing and addition of the antibiotics each day after a big water change, as you've been doing, will assure complete recovery. Did you go a full 10 days?