Platys Dying Need Help!

[Spinnerwolf]

Hello Everyone!

I am about as new as you can get to having fish. My current problems are centering around my platys and I could really use some help. I first started encountering issues about a week back. At that time I had three platys and a Betta fish in the tank (they had been in the tank for two weeks). Two of those original platys have passed away, the third is still thriving. Besides those two i have had multiple others die and the behavior of the dying fish has been very similar. Their swimming appears very irregular (seems like they can't control themselves, bumping into things, quick bursts of speed and near the end listless drifting), they are up at the top of the tank gasping for air after this point they die within a couple hours. The addition of a second air hose(with airstone) seems to aid the issue but i get the feeling this isn't the real fix just something that is helping until I can find out what is wrong.
I did discover a couple days ago that the water was on the acidic side(6.2) but that has been corrected for a while and now two more platys are behaving irregularly again even with a second air hose.
The tank:
5g
Still cycling, current values are
Ammonia: 1.0
Nitrite:0
Nitrate:5
Water hardness:soft
Alkalinity:120
ph:7.2
Tank has:
1 crowntail betta
four platys, similar size and no signs of infighting.
Tank temperature:76 Farenheight, 24 Celcius
Tank has been cycling for about a month, this is my fault I had no idea what cycling was and when I purchased it the guy at the pet store claimed it would be perfect for a couple fantail goldfish i bought at the same time. Anyone who knows anything about goldfish knows how very wrong that is. I bought a new adequately sized tank for them and they are luckily doing fine with a lot of TLC.
The reason the 5G it is still cycling is because I was changing too much water whenever I was attempting to keep values within a range where it wasn't causing harm to the fish. This was a beginner's mistake...I feel really bad about it.
I really appreciate anyone who takes the time to help out a newbie, I know i've made mistakes but I am really trying to learn and I'd appreciate any help to keep these little guys from getting hurt or dying.


To clear up the first possibility early on, the betta is not killing the platys. He has been with this type of fish now for about a month, he does not puff up on them or attack them, he keeps to himself. (I kept a very close eye on this, if he were hurting them he would have been removed.)

 

[WILDER]

I'm afraid your tanks overstocked for a 5 gallon. A rough guide is one inch of fish, to one gallon.
The reason why your fish are dying is due to bad water quality. Ammonia poisoning. Get you some information. When a tank is overstocked the filter won't be able to cope.
I would maybe think about getting the betta a tank of it's own.

For now immediate water change. Increase aeration.
Add one tablespoon of salt to the tank. Get a jug of tank water. Add the household salt. Stir the water till the salt has dissolved.. Add to the tank.

I would do your own research on fish before you buy. Tank size, adult size, compatibility.
2 fantail goldfish would need at least a 36 gallon tank. Also they are massive waste producers so need double fileration.

Link
Ammonia poisoning.
http/www.fish-disease.net/diseases/ammonia_poisoning.php

 

[WILDER]

How long has the goldfish tank been set up please. As wondering if you could take some of the filter sponge to add to your 5 gallon filter.
How many gallons is the goldfish tank?
Sorry I missed the part about buying the 2 goldfish.

 

[Spinnerwolf]

Goldfish tank has been set up for several weeks now, 30G still cycling but the goldfish are doing fine, I have done a lot of research on them they get spare bits of orange for a treat as well as peas and blood worms with their usual soaked flakes. What I need is info on the platys though, the goldfish are fine for right now though I appreciate the suggestions
Filter sponge isn't really removable it's the cartridge kind, it would be hard to get a piece from.
I am pretty sure it isn't the ammonia, i have been performing regular partial water changes 10-20% to keep the ammonia at 1 or lower. I though ammonia poisoning starts at higher levels then that?

 

[WILDER]

Darting. turning upside down, being listless and lethargic, gasping,red streaking,unable to maintain balance in the water, spinning in circles, red inflamed gills, lilac gills. Are all symptoms of ammonia poisoning.
It takes a really hardy fish to get throw a cycle. It best to do a fishless cycle as it to heart breaking watching the fish suffer.

 

[WILDER]

http/freshaquarium.about.com/cs/disease/p/ammoniapoison.htm