Tank problems...I have no clue what I'm doing now

[Greendragon1128]

Everything was going well--tank slowly being stocked, all fish seemed healthy. Then one of the platies caught fin rot, plants started dying, and one of the plecos has a white spot on it. Also, I thought I had seeded the 10g with filter media from the 47g and had about ten platy fry in it, but the ammonia started to increase. The fry are now back in the 47g, and I'm doing a proper cycle in the 10g.
The fin rot has spread to the 2 pregnant female platies, and the pleco hasn't come out of the cave. I have a bad ratio of guppies, and the 3 males won't leave the femal alone. My Brazilian swords have lost pant of their roots, and the smallest one died. I have treated the tank with Lifeguard All-in-one treatment, starting yesterday. No signs of improvement yet, but it might be too soon to tell. Also, the problems started when I put in fertilizer tabs--could this be causing the diseases?
If my tank is beyond help at the moment, the healthy fish and plants can stay in my friend's 35g for a while. I hope I don't have to do this, though.

Thanks in advance!

 

[brian1973]

I would only move the known sick fish to a qt tank, moving seemingly healthy fish to a healthy tank could cause you to spread the illness to your friends healthy fish. I have never had any issues with ammonia when using established filter media. I would get rid of the female guppy because the males may kill her by pestering her to death. I havent had any plant related problems yet so I cant help you there either. I have had succss with quickcure but that was for ich and I dont know if it works for finrot.