Maroxy is more of a topical antiseptic/disinfectant, as stated in the link it's chlorine based. Maracyn is erythromycin, an antibiotic which is effective with most gram positive bacteria, and some gram negative bacteria. Maracyn II is a tetracycline based antibiotic, effective against gram negative & some gram positive bacteria.
There may be a bit of confusion in product names here, as Mardell does produce Maracyn Plus, which is a trimethoprim/sulfadimidine combination, more commonly sold as TMP sulfa. This will cover much of what using a Maracyn/Maracyn II combination would, being sulfa based it is more effective on some bacteria, less effective on others.
Maroxy is a good product for hatching angel eggs, been using this in combination with acriflavin & meth blue for years. For fish you could have the same effect for free, using chlorinated tap water. As far as columnaris & Mardell products, if your using Maracyn & Maracyn II, 50% water changes daily & redose, for 10 to 14 days. Wait for 10 minutes before adding dechlor to the replacement water, you'll have the same basic effect as Maroxy.
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