Fish Is Dying, Help!

[joeynuna]

I have a 20 gallon tank with 5 mollies. 1 molly is an adult and 4 babies. I had 6 mollies and one of the babies died last night. The adult molly has been ill for at least two weeks. At first I thought it was swim bladder. I fed her peeled peas. She began to improve and then she took a turn for the worse. She lays on the bottom of the tank, sometimes eats, and once in awhile she will swim. Now, one of the other babies is showing the same symptoms. I have no idea what to do. Help!

Note: About 2 months ago I added painted aquarium safe rocks. I feel it may have something to do with the problem. They have since been removed from the tank. If it is toxic poisoning, what can i do to save the fish?

Please do not reply with "too many mollies in tank." They're still babies and i'm finding homes for them. I've given away about 27 so far. The tank is not, and has not, been overcrowded. I have 10 gallon tanks, fully cycled, for the fry.

no signs of ich
no signs of any other illness

My habits:

I use prime for my water changes.
I do 20-25% changes every week including gravel vacuum
Filter - Bio wheel 200 (200 gph)
I add 2 tablespoons of API freshwater salt with each water change. Some people say not too, use marine salt. I don't think this would contribute to my fish dying. But, who knows.

Ammonia - 0
Nitrites - 0
Nitrates - 10
PH 7.5
KH - 4
GH - 8
Temp 80

 

[LauraFrog]

Hmm... this is odd. How big are the baby mollies at the moment? Is the adult fish too skinny?

 

[WILDER]

Do the fish look skinny or bloated.
What does it look like when the fish go to the toilet.
Is the enus of the fish enlarged or red and inflamed.
Do any fish swim on there sides.
Lost any fish to bent spines.
Does the fish look pale or darker in colour.
Are the fish still eating.
Is the fish tilting to oneside.

 

[joeynuna]

Do the fish look skinny or bloated.
What does it look like when the fish go to the toilet.
Is the enus of the fish enlarged or red and inflamed.
Do any fish swim on there sides.
Lost any fish to bent spines.
Does the fish look pale or darker in colour.
Are the fish still eating.
Is the fish tilting to oneside.

Thanks for the reply. She died the other day. The rest of the tank is fine. What do you mean by "lost any fish to bent spine."

 

[WILDER]

R.I.P.

If the spine looked bent, as it can be a sign of old age, vitamin deficiency, fish tb, internal parasites, injury.