dead fish!:(

Question
So ijust started a new tank. my boyfriend bought it for me for my birthday and i encountered several problems. the first set of fish came from the local walmart, one died. the first that died from that bunch was a pleco, i assume someone ate him because he had alrge chunk missing from him. then i went to petsmart and they told me the fish may have been unhealthy, and got eaten afterwards, now i bought another pleco, and two mollies, amomg other things. this was about three days ago, now both mollies are dead and the molly from walmart is now dead as well. i am so frustrated and devastated.are mollies prone to any type of disease? two of the three were generally active, very active and friendly, the last one was quite timid and only enjoyed the company of my betta, but wen i intriduced the new mollies it became very active and more outgoing. my water temp. is usually, 80-82 a few times i caught it on 78 and i changede it. please any information would be great. my betta is no longer in the tank and i suspect it may   be that they were sick from the start but i observe them very closely and no results from internet searches as turned up anything. i hope i have provided u with enough information and thank you for ur time.

Answer
Hi Diana
Sounds like your tank's going through what's called "new tank syndrome".  Basically what happens, fish produce ammonia through their waste and respiration.  A beneficial bacteria develops that consumes the ammonia and converts it to nitrites.  Both ammonia and nitrites are very toxic to fish.  Another beneficial bacteria develops and converts the nitrites to nitrates.  This whole process is called the nitrogen cycle or the cycle process of a fish tank(do a search on both of those terms).  The whole process takes on average, 6-12 weeks to complete, it's also known as your biological filtration, which if you read any further on this, you'll see mentioned quite a bit.  Here's a link that explains all that a bit more in detail:

http://freshaquarium.about.com/cs/biologicalcycle/a/nitrogencycle.htm

If there's no more fish in the tank, I would recommend doing what's called a fishless cycle.  Basically all you do, pick up a couple of frozen cocktail shrimp from the store.  Put them in a pair of nylons/pantyhose with the foot cut off and knot it closed.  Toss it in the tank and let it rot.  This will produce ammonia, starting or rather continuing the cycle process in your tank.  Don't do any water changes, just let the tank be, and top off any water that evaporates.  If you don't have one, pick up a test kit that tests for ammonia, nitrites, nitrates, and ph.  I recommend the liquid dropper test kit by API, has all those tests and costs about 30. at the pet store(can buy them online cheaper, I usually buy stuff through drs. foster and smith where it's only about 15.).  With your test kit you'll mainly be testing the ammonia and nitrites at first.  First the ammonia will spike high, then start to drop and nitrites will show up and spike.  When the ammonia and nitrites spike then fall to 0 ppm, and there's some nitrates present, the tank has completed cycling.  When you're ready to add the fish, remove the shrimp, do water change to get the nitrate levels down below 20 ppm(where you always want those levels to stay), then slowly add a few fish to the tank.  Then give it about a week or so before adding a few more fish.  By a few, I mean only 2-4 depending on the types of fish and your tank size.

You don't mention what size tank you have, but do be aware that the more common pleco varieties that are sold have the potential to grow over 12 inches, and are therefore not compatible with most tanks, definitely nothing under 55 gallons.  So, be sure to research any fish you plan on buying before hand, and dont' trust the pet store employee's advice.  Also, Walmart is generally not the best place around to buy live fish from.  They're a general merchandise store, not a pet store-even a lot of pet stores aren't the greatest either....especially where I live lol....

Best thing to keep in mind since you're new to fishkeeping, do your own research before hand-there's lots and lots of info out there online, have patience, and take it slowly.  Trying to rush through everything and doing it all at once only leads to disaster.  

Hope that helps and good luck!  Let me know if you have more questions.

Christy