fin rot help please

Clean water! With a case this severe, you're going to need to put the fish in a hospital tank, treat with anti-biotics, and do DAILY water changes, since the medication will nuke the bio-filter. You need to start more maintenance on the main system--99% of the time, these types of infections are related to poor water quality, or too much stress from tank mates.
 
It was a new fish, in a QT. The other one is completely fine. The one that is sick was in a plant yesterday, but the just the end of the fin was a kinda clear looking. When I got up this morning the tail was gone. I put a divider in the tank. What % water change should I do--they are in a 10 gallon?
 
How long have they been in the QT? What species are they? What filtration is on the tank?

The divider is great. I'd plan on doing 50% changes daily--especially if the QT didn't have an established filter when you put them in.
 
They are African Cichlids. The one that is sick is a red zebra. They have been in there for 2 weeks. I checked ammonia and there was none detected (I use liquid test) I did a water change a couple of days ago.

The med I bought from the LFS is Mardel Tetracycline Tablets. I just went to do a water change and medicate, but the meds are expired--April 2005. I am going to take them back. I do not like the store, but it is the only one. What should I do if all they have is expired?
 
Do the water changes, and hope. I'm not sure how effect salt would be, but that's another treatment option. Might want to check with folks more familiar with cichlids, too, and make sure the water parameters (hardness, pH) are within range--some african cichlids are less adaptable to changes than others.
 
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