Return of mysterious platy plague

[Greendragon1128]

My platies are sick and I don't know what's wrong!
I just got back from a weekend trip to see two of my platies hovering near the surface, fins clamped to sides, wiggling back and forth. One is missing a chunk of his tail. I performed a water change last Thursday because of high Nitrates and some Nitrites. Earlier that day, I euthanized a platy that showed the same symptoms earlier in the week and at that point was floating almost vertically in the corner behind the filter.
The first deaths were a couple of weeks ago. I thought it was from high Nitrate levels and did a water change. Now I remember that this was right after I had gotten plants from the LFS with dead fish (my dad was in a hurry so I didn't have time to thoroughly inspect the tank like I usually do).
I first noticed problems (one dead guppy) a couple days after buying a swordtail and platy from a different LFS with seemingly healthy fish. They are fine, so I don't think they caused any problems. I think the disease started with the first platy deaths, but I didn't realize it at the time or I wouldn't have gotten the new fish.
I haven't added any medicine, just salt and heat. I'll check ammonia, nitrate, and nitrite and post the results.
Thanks for any help.

 

[Lotus]

Your water parameters will definitely help rule out water quality problems.

It's possible your tank is infected with some kind of bacterial disease, but it's best to post your water parameters in case that's the problem.

Increasing heat, if it's a bacterial infection, can cause the disease to progress faster. Salt and heat is really only useful for treating ich.

 

[Greendragon1128]

Ammonia between 0 and .25, Nitrites 0, and Nitrate 5
One of the platies didn't make it through the night. The other is hovering under the breeders box (I have swordtail fry) and seems to float back to the surface every time he swims down. He is gulping at the water and wiggling his head violently. At this point, I may euthanize him before he infects the rest of the tank.
I treated with salt because the package said "use as general tonic" and it seemed to help. One other fish was acting a little strange before the w/c, but he is fine now.
When I had this problem before, it was one of my oldest fish who was probably at the end of his life expectancy. All the platies I have now have been born in my tank. The oldest (the sick fish is one of these) were born at the end of August last year.
I turned the heat back down, but the dank is on an outside wall in the room that isn't air-conditioned. The temp. is staying around 80.
Thanks for the input.

 

[Greendragon1128]

I euthanized the poor platy before he could suffer any more. Everyone else seems fine, so I'll just moniter it for a few days. I also did a partial water change to help remove whatever is causing this.

 

[1077]

In a mature or (cycled) tank ammonia, and nitrites should read zero all day every day. Is possible fish are suffering from nitrite poisoning.Ammonia spikes are probably occuring as well. I do not know what type of filter you have on your tank but assuming that the filter is large enough and contains healthy bacteria colony and you are rinsing the filter pads,cartridges,etc out in old aquarium water or dechlorinated water (NOT TAPWATER) during weekly 20 to 25 percent water changes,, You may need to add an additional filter to run along with the present one. I would also reduce feedings to once a day and only feed as much as you actually see the fish eat in one minute.
Platys and swordtails prefer cooler water than guppies or mollies and also prefer hard slightly alkaline water withv pH values of 7.4 bto 8.0. Platys and swords would appreciate water temps between 74 and 77 degrees while mollies and guppies thrive in temps up to 82 degrees.Salt will help detoxify nitrites and also helps with ICH , but other than that ,freshwater fish really don't need it and some fish are quite sensitive to it. If your pH is 7.2 or lower. marine salt would be more helpful for the livebearers than aquarium salt. The marine salt contains minerals that help boost and maintain alkalinity but this isn't needed unless you have very soft water.
Is also possible you are introducing sick fish from the outset to your tank. I would consider a quarantine tank for any and all fish that I purchase so as to prevent ,or at least help prevent possible parasites or pathogens from being introduced to my tank and possibly infecting healthy fish. Most recommend(me too) ,quarantining fish for ten to fourteen days before introducing them to your tank. This will help a great deal with keeping your tank disease free.
For now,, I wouold perform daily small water changes to get nitrite levels to zero using a dechlorinator such as PRIME for treating the new water before it goes in the aquarium and take care to add water that is close to same temp as water in your aquarium. Hope some of this helps.

 

[Greendragon1128]

Maybe I should have also mentioned:
Temp: 80
PH: around 8 (I only have drop tests for ammonia, nitrite, and nitrate, unfortunately)

Unfortunately, the tank is on an outside wall in the room with no a/c, so I have a hard time keeping temps down in the summer. It usually stays around 78-80 year-round.

The filter is an Aquaclear 50 that I think is powerful enough, judging by the way it "ate" half-grown guppy fry before I put some netting over the intake. I haven't changed the filter pad since February, just swished it in old tank water as I dumped it out.

I will go back to treating water one bucket at a time during water changes. I use AmQuel and NovAqua, but will look for PRIME at the new LFS I discovered. The problem may be that I haven't been doing weekly water changes, more like monthly. I'll do more frequent changes, but this is going to be a major headache during marching band season. Would anyone like to take care of my tanks September-November? jk, I'll just have to learn to do my homework faster.

The quarentine tank may be a bit of a problem, though. My parents just laughed when I suggested it. Would a sponge filter in a rubbermaid container work? Then I'd just have to figure out how to keep the cats from seeing it as a gourmet seafood dinner.

Thanks for the input. The tank seems to have stabilized (from the water changes?) so I'll just watch it for a few days.