Problem with Mollies

[xGerrard]

Recently purchased a 21 litre tank, inside i have 2 black lyretail mollies and 2 dalmation mollies, each fully grown, then i have about 14 various fry's which are not at any risk of been eaten as theyre large enough. Within two days the dalmation mollies both died, i think they were both male. I took them to my lfs with sample of the water and they said it was fine. They replaced the fish with two females which seem to be doing fine in the tank now. I bought a moss ball and placed that in my tank. The two black lyretail were both lying on the floor of the tank, i told them at my lfs and suggested buying an air-rock, which i have, one of the black lyretails are now fine, swimming around the tank fine, however the one is still lying at the bottom, I've fed it and it swum around a little but now it's still occupying the same place. Anyone know what it could be?

Also another quick question, a few of the frys seem to be wedging themselves inbetween the stones and the glass, they are getting out, but some have been there a while, is this normal?

 

[Matt68005]

Your tank is much too small for that many mollies. They can get big. Im not saying it has to be a huge tank, but with a 5.5 gallon tank your options are really limited....
I don't know why mollies do that. Mine use to hang out mostly near the substrate even swim along the bottom to look at me and then come up to feed.

 

[xGerrard]

The fry's will only be in there for a while, my friend's fish gave birth to them and he gave them too me, when they're a bit larger so I'm able to sex them I'll sell them, I also have 2 10 liter tanks which I'll be putting two females and a male hoping to breed within each.

However my main concern was the lyretail mollie lying on the floor. It swims around rarely, staying towards the bottom of the tank, and then goes into the same place not moving seeming to 'breath' rapidly. I have tested the water conditions, took a sample to lfs and they said it's fine also, i do treat the water with a table spoon of salt every water change as i know mollies like that and at the moment that's all im keeping. Just slightly worried about the lack of movement thats all, hoping someone can help me?

 

[Matt68005]

Im not trying to put you down or pressure you. But sailfin mollies can get like 4 inches long easily, and have drops of up to 200 fry from a single mature female. I love guppies and i like mollies, but guppies would be better suited to such small tanks, maybe then even the small wild ones.
As far as you "bug" my best guess would be nematodes. Fenebendazole is a dewormer used in fish, but it dosent "kill" the worm, just paralysis it. Praziquentel might work in a pinch. I know its hard to fins meds in the UK and Aus. So im trying to stress to you to just get a 41 liter tank at least and keep it clean. The salt is great idea, but if its table or marine salt, you must stir it well to dissolve it or else it will burn their gills and eyes. A 75.7 liter tank is usually the reccomended minimum size for mollies. You defintaely want to do at least half that.
Now on to what caused the stress. Poecillia, both mollies and guppies, will chase females to death. You must keep a 1:3 or 1:4 male to female ratio. Stressed females get sick. Do not feed tubifex or any other live food. That is how internal parasites get introduced. If you wanna go "outback" then buy some frozen or freze dried worms or brine shrimp.
Im not saying you do any of this or dont already know half of this. Just trying to outline some good advice for you and others. I struggeled with this internal "bug" that has been going around in livebearers for a long time. I talked to a long time professional guppy breeder by the name of Jim Alderson, (who like me loves to specilize in diseases and water qualtiy/tank setup) and he said Poecillia normally comes down with Callapari or callamunus nematode worms. You may see red round worms on the anus of the fish, or i think callapari is miscroscopic. Mollies also like alot of algae in their diet, heck buddy he may just be constipated....lol
Some fish are just more prone to certain diseases than others. Some people will give you bad advice saying its Fish TB or Hexitima, when in truth poecillia is more prone to worms and bacterial problems than anything else. Has alot to do with where the fish come from in nature and the water and environment temp ect. They build up resistance thru survival of the fittest for millenia, then in a few years they are bred in diffrent water and inbreed to make cool colors and next thing you know you got sick fish all over the place.