red lines in the tail of my red cap goldfish.

Question
QUESTION: sir,
i have a red cap goldfish and it has been continuously
developing red lines in its tail, they are like blood type.i
got my water tested reading your FAQ'S and had a nitrate
problem.it was regarded as unfit for drinking.so, could i
get some knowledge on what should i do to prevent those red
lines.i always dechlorinate my 20% of my tank every week.

ANSWER: Varang,

 I think your fish is suffering from septicemia, a blood borne bacterial infection. I would do a large water change and start treating the fish with an antibiotic. The best is the brand name Furanace, or you can go with  Maracyn 2. I would also feed him a medicated food. Follow the directions on the bottle of medicine and continue to treat for 14 days. Your water is toxic to your fish.

---------- FOLLOW-UP ----------

QUESTION: sir,
so would this antibiotic do any harm to other fishes i have in
my tank??
i have 2koi,1 oranda gold,1 copper gold..so what should i do
with my water??i dechlorinate it regularly..stil it is toxic??

ANSWER: Varang,

 Using the dechlorinater is a great start. You tanks problem is what happens after the water has been in the tank. You have 5 fish in  your tank. I am hoping your tank is a minimum of 300 gallons. If it is any smaller, that is your water problem. Goldfish are the messiest fish. They do not have a stomach, so everything they eat comes out as waste and quickly turns into Ammonia. That is why your fish is sick. Its not the chlorine thats the problem, its AMMONIA, NITRATES, and NITRITES which are bad for fish. Until you get the water problem fixed you are going to continue to have problems. Koi fish are not meant to be in aquariums. They can grow up to 3 feet long. They belong in large ponds. Your tank will always be toxic with the fish you have in there. I would make sure you have a very large filter as well. You need better filtration for the fish you have. I would treat the whole tank, since they are all in the bad water. If one fish has this problem, guaranteed the others are not far behind.

---------- FOLLOW-UP ----------

QUESTION: thank u sir,
so what is the survival rates of the red cap?? would it be
saved by timely cure or remedies or the disease septicemia
is difficult to cure?? my two goldfish too died like this
and i dont want any fish to die again...moreover would a
better biological filter help with the water problem??or i
need to get my water treated?? earlier i was using melafix
for the tail rot the fish had caught it was not of good
help.. i have a 2 feet  long, 1 and half feet tall and 1
foot wide.. i holds nearly 51 liters water approx..
thanking u in anticipation.
you have been of great help.

Answer
Varang,

 First off, your tank is only 13 gallons and grossly over populated. Let me break it down for you to help you understand.

2 Koi need a minimum of 200 gallons just for them.
3 goldfish need a minimum of 60 sixty gallons.

This is the absolute minimum, and would be best to have a much larger tank. If you treat the red cap with the right medication and as soon as possible, survival rate is good. The best way to keep this from happening is better water quality. The key to helping your fish is to find out what caused the problem and fixing it. There are a lot of good water conditioners out there and they all work the same way. Prime is an awesome water conditioner and is available everywhere. Unfortunately, if you don't fix the water issues, then you will have more dead fish. Yes a better filter will help a great deal, but no matter what type of filter you have, you will still need to do 25% water changes every week. I would give him a salt water bath, instructions below.

SALT WATER BATH (DIP):

 Get a container that can hold 1 gallon of water the same temp as the tank water. Add 1 teaspoon of aquarium salt that has been dissolved before adding your fish to that water. If you don't dissolve it first it can burn your fish. Let him swim in this water for 5 minutes the first day, both times, 10 minutes the second day and 15 minutes the third day and every day after for 5 days. watching him closely the entire time he is in there. I want you to watch him in case he starts to have a problem, you can remove him from the salt water immediately. I would do this 2 times a day, but never in the same water. Always make fresh salt water every time you put him in.