[How long should I wait after Columnaris outbreak?]

After a long battle with columnaris, I lost 10 of my 12 guppies. 😞

They were in a receiving tank and went through one round of ParaCleans, Ich-X and Maracyn, as well as two rounds of Maracyn Two, and aquarium salt. The surviving two are doing great, but I am very hesitant to stock anything else. 

What is a good time period to wait to ensure that I don't get another outbreak?

 

Thanks! 

[Adding Maracyn to salt treatment ok?]

Works for me, thank you!

[Adding Maracyn to salt treatment ok?]

I got 12 new guppies to restock an empty 24gal aquarium from both Petsmart and Petco. 

While in the 10gal receiving tank I ran one full application of Paracleanse and had just started a round of Ich - X (I didn't know I could apply them all together at the same time...) when two of the males began having a hard time swimming, and one of the females began to get a white patch on her back (Pics). I went to start a treatment of Maracyn, but realized I bought Maracyn Two instead of the regular. I ordered it promptly but all three died the following day, and a second female got the white patch. 

This last Thursday I started treating them with salt, at 1Tbsp per 2 gal of water. This seemed to clear up the white patches, but the guppies still got lethargic and died... 

As of today, 3/13 I only have two guppies left and the Maracyn just came in. 

Is it ok to add Maracyn during salt treatments? Or do I need to start water changes?

What else could be affecting these guppies?

Thank you!