Pot Bellied Mollie Death

Question
We bought a 12 gallon eclipse aquarium for Christmas and are first time fish owners.  We got 4 pot bellied Mollies on the 29th of December and have managed to keep them all alive until today.  I was devastated to find our orange one, Sharpay, at the bottom of the tank underneath a plastic plant dead.  She had babies the day after we brought her home and one managed to survive.  Sharpay seemed to be doing fine.  I have been monitoring the nitrates and ammonia every other day and the nitrates have been at zero and the ammonia has been at the stress level but we can't get it down no matter how many times we change the water.  The other fish seem fine, even the baby fish, and I am wondering if Sharpay could have gotten stuck in the plastic plant which was new to the aquarium (only in two days).  She was laying on the rocks at the bottom of the tank under the plant but she didn't seem stuck.  When I pulled the plant away from her though, her body floated up. So I was wondering if she could get stuck in a plant or if fish sometimes do sink to the bottom when they die?  Also, do I need to change the water since she died in there.  I immediately checked the ammonia and nitrates and they were the same as always.  Do you think maybe she was old?  She didn't seem old but I don't know how to tell.  We also haven't changed the bio-wheel filter yet but it don't seem that bad.  I took out the plastic plant (there are two other smaller ones that have been in there since the beginning) but I am just not sure if that was what killed her.  If you have any information or idea of what could have happened or what I am doing wrong I would love to know before we have any more casualties.  Thanks!

Answer
Hi Melisa. Sometimes fish die after having fry for no apparent reason, so this is most likely what has happened.  I'm going to also give you a link that will explain the "cycling" process a tank has to go through in order to sustain life, so it should help you in helping the tank get through cycling. Typically you wouldn't use this type of fish to cycle a tank, but if you are very careful they may make it ok.  But then again, you could very well lose all of them through the cycling period.  The link is: http://www.americanaquariumproducts.com/Nitrogen_Cycle.html

Follow what it says and you should be ok.

Good luck!  ;o)