tail damage and brown spots

[noelberg]

During feeding my mail swordtail had this thing that kinda looked like a small snail on the sword part of his tail, but it definitely wasn't since I haven't had any snails. About 30 mins later it wasn't there and a tiny piece of his tail was missing where it was. Today the tail is sort of flaking away and he isn't as active.
I plan on using Melafix, but anybody have ideas?

Plus I also found out that I have reddish-brown specks on my rocks and pebble substrate. I removed a rock for cleaning and the spots smudge off. I feed small amounts twice daily, my pH is 7.8 (high, i know - I'm doing a water change), no nitrItes, trace ammonia, and I'm getting a nitrAte kit today to test that. My tap water's pH is between 6.8-7.0. My bioload might be high eventually (and I'll get a new tank) but right now my inches of fish are about 20 in a 20 gal. I've got a biowheel 125 gph and a bubble wand. The tank gets a small amount of natural sun in the morning. I have cories to clean the bottom, and I have 2 java ferns. I got my rocks from a fellow fish enthusiast, not a store, so I have no idea what they're made of.
Any help would be greatly appreciated.
Thanks in advance!

 

[noelberg]

The male and some of the other swords are flicking against the java ferns, not the rocks, but just the java ferns. Not frequently, but every once in a good while. Dunno if there is a parasite in the water. I've had HORRIBLE luck with Swordtails

 

[snowyangel]

Did you say there's a trace of ammonia? Because any amount of ammonia is lethal to fish . I think its your ammonia and your pH thats irritating them and causes them to flick. If you start seeing white specs on their bodies, then you have ICH. Read this on common diseases

 

[noelberg]

Thanks for the advice snowyangel.

I did a large water change. I think one piece of rock was actually coral because my friend told me YESTERDAY it was from his old marine tank
Cutting down feeding to once per day, and I had to take pity on the poor swordtail and euthanize him because he wasn't moving (resting on bottom) and his entire caudal fin (and some of his body next to it) rotted off in less than 48 hours. Added Jungle anti-bacterial/fungal tabs and the rest of the fish look extremely healthy.