1. How big is your tank:  Gal / litres     30 Gal

2. For how long has the tank been set up:  9 months

3. How many fish: 3 Comet Goldfish and 4 Japanese trapdoor snails 2  freshwater plants and one Bamboo

4. What kind of fish:  3 Comet Goldfish  1 fish is 2 years old the other two are 9 months

5. What are the water parameters:    Ammonia.........ppm   1. 0 ppm  API liquid kit
                                                            Nitrite..............ppm  0 ppm  API liquid kit
                                                            Nitrate.............ppm  N/A
                                                            pH..........................  N/A
                                                            Temp...............degrees Celsius / Fahrenheit   70 f

6. How often do you perform water changes: Every two weeks

7. How big are your waterchanges:      ..............  25-30 %  I also add aqu salt

8. What kind of waterconditioner are you using:  Aqueon

9. Do you add beneficial bacteria: Bio Trace

10. Symptoms your fish is showing: One has a split tail right in the center of the tail all the way to the base it is bloody then it has white around it. 2 nd  fish has one small sort of fuzzy white spot on the top of its tail. The third is showing no signs.  I have been doing a water changes first thing in the morning for the past 2 days taking 40 % out of the tank. I have taken the carbon out and started adding more salt, Pimafix, and Melafix. My Ammonia is not going down. I put the snails in a different tank.
 My water a couple weeks ago had a brownish brackish tinge to it fish were acting normal. The Nitrite was elevated to . 25 ppm I had to move my tank so we did a 60% water change and changed the filter pad after soaking the new one in aquarium water with the old pad. Ran test on Ammonia and Nitrites reads went back to normal water was the clearest I have seen it in a long time. Now fast forward two weeks and I see my fish with the split tail reads on Ammonia is elevated. Me in panic mode.

11. Since when does your fish show these symptoms:    2 days

12. How is the normal behavior of your fish: Happy swimming around begging for food

13. How do the other fish behave: the same

14. Post pics of the sick fish:


 

15. Do you have a filter on your tank, what kind, how big (gallons per hour)  EHEIm 2232  up to 35 Gal

16. Do you provide extra aeration with an air pump and air stone/diffuser of some kind. Yes Air Stone 40 Gal

I will check out the prime. I misspoke I use Aqueon for water conditioning  to treat the water and salt every time I change the water.

It seems perfectly fine to me, you're on a good way to repair the mistake However, stop adding salt when the fungus goes away Goldfish aren't alt water/brackish fish, so they don't need the constant addition of salt. It could hurt them instead when adding it on a bi-weekly basis, since there's only more and more salt accumulating over time.

Also, a part of the problem could be that you changed all the filter media just like that, rather change half at a time, and you don't need to do that very often. I've had my external filter running and I just changed the thin wool pad since it was getting soggy after several month of use. Never changed on the internal one, and I've had that for more than 6 months by now.

Be careful with the ammonia! You may want to add some zeolithe to the filter in case of emergency, but the beneficial bacteria should do the trick! The symptoms your fish are showing don't seem very serious at all, a torn fin usually heals all on it's own in good water, so focus on using gentle medications, such as salt and mela/pimafix so that you won't disturb the beneficial bacteria, and add A LOT of bio-filter booster!!

Good luck, keep us updated!