Fungus? Parasite?

Question
Hi there,

I recently had a fish death of a possible fungus or parasite.  It was my only fish (a very small molly) in a planted 5 gallon tank with 3 cherry shrimp.

Do I need to completely break down the tank? or Medicate it with something that is shrimp/plant friendly? before I try putting another fish in there?

How do I sterilize for something that I don't know was the cause of my fish's death.

I'd rather not have to break down the tank because the plants are quite happily rooted.

Any suggestions? that are plant and shrimp friendly?

Thanks.

Answer
Hi Jennifer,

I do not recommend medicating when you are uncertain of the cause. While there are some "medications" like Melafix and Pimafix, their efficacy is questionable. It is more of a preventative, it will not combat a viral or bacterial outbreak the way antibiotics would.

I would not break down the tank. Check the water parameters, ammonia and nitrite should be 0 ppm (in a healthy, established aquarium this is always so) and nitrates should not be over 20 ppm. Mollies are especially sensitive to nitrates, especially if they are kept in entirely fresh water without any salt added to it. They also need water that is hard and alkaline, with a pH of higher than 7 and a hardness and alkalinity that is moderate at least, preferably high. An alkalinity level that is low causes pH to dip down, which is awfully stressful to a hard water loving fish such as a molly - or any livebearer, for that matter. You can read more about that here:
http://www.wetwebmedia.com/FWSubWebIndex/mollies.htm

Keep an eye on everything, do water changes every other day if anything is off (such as a pH lower than your tap, or high nitrates) and eventually everything should be back in line.

"Sterilizing" your tank would be undesirable, because your tank would no longer be cycled, you would have to reestablish the nitrogen cycle. Instead, wait a while before adding fish.

If you are in a hurry to restock with fish, look on the back of medications at your local fish store or pet store and get something that is labeled "invertebrate safe" - the article below has some suggestions:
http://www.aquariumfish.com/aquariumfish/detail.aspx?aid=21399&cid=3788&search=
Take a look at the second question down.

I hope that helps. Take care, and have a nice weekend!
Nicole