BurgosRL;4747145; said:
Bu the way, I am new to this hobby and have been wanting to do this for years!
I love your enthusiasm
I am not sure how long you let your tank cycle before adding fish, but I am guessing by your reply that it didn't have time to complete.
There are thousands of posts here on MFK and even more discussions on the Nitrogen Cycle of an aquarium. I will give you the condensed version:
Fish produce waste. Waste produces ammonia. Established bacteria in the tank (mostly in your filters, substrate, etc) will oxidize the harmful ammonia. The bi-product is nitrites, also a toxin. Other established bacteria will convert the nitrites into nitrates. The only (convenient, affordable) way to remove nitrates is to do partial water changes. Your cycle is now complete and will start over.
Again, that is the very basic, condensed version. I beg you to search, read and research more on the Nitrogen Cycle. Understanding it will make you a better and more successful fish keeper
So now, I assume you actually didn't have a fungus. It sounds like the fish introduced into the tank were too much for the bio...or lack of bio actually. Since the bacteria wasn't established yet, ammonia levels built up and your fish died. "Clear" water isn't necessarily healthy water. You need to get a test kit and actually test, primarily, for ammonia, nitrites and nitrates. These kits can be expensive...but most fish stores will test your water for you for free.
But, you have to still be careful. If your tank hasn't gone through a complete cycle, you could get good readings simply because you haven't had fish in there generating ammonia. Another case is, even if you have cycled, you don't want to dump a boat load of fish in all at once...your bio won't be built up enough to handle the insurge of waste.
Now, back to your tank. Very few here use chemicals to jump start their tank. For the most part, we've all made similar mistakes, but by our 3rd or 4th tank, we've learned patience

Its best to let your tank cycle naturally.
To start with, I suggest you do a 50% water change right away. Make sure you use a de-chlorinator on replacement water ("Prime" is HIGHLY recommended!)...or let the water sit for 24 hours with a bubbler running in your storage tank.
Most keepers here don't use carbon in their filters but opt for the most bio possible. In your case though, I would run some carbon in your filter for two weeks or so to get rid of any leftover medication. After two weeks, remove ONLY the carbon cartridge and replace it with another bio cartridge or mechanical cartridge if bio isn't available. Somewhere along the lines, your ammonia will begin to climb, then drop off. At this point, your nitrites will go up...and drop off. Then watch your nitrates. Once they get to around 20ppm, do a 50% water change and check it again. At this point, you can start adding fish if everything checks out
Sorry for the lengthy reply, but trust me, I didn't even scratch the surface! Once you get the tank cycling, take time to read and research. You'll see what I mean lol
Post back with questions. The people here are extremely knowledgable and helpful. You can get pretty much any question answered here.
Good luck! See you around the forum...