My fish have white spot how can i cure it

Question
I have a large tank and bought about 30-35 goldfish and other fish, but after 2 weeks they all got white spot and i lost all of it. After that i empty the fish tank and clean it with hot water and every thing i put inside and put it dry for two days, and after that i bought about 35 fish again but after 3-4 days the same symptoms appeared i dont know what to do i used undergravel filter, automatic heater etc i've done everything i know but its all a waste please help.....

Answer
Hi Issac,
Your tank must cycle first before you put any fish in it.  Ask your pet store for used gravel from an established tank.  One handful is enough to add good bacteria to your tank.  Let the water run for about one month, with NO fish, adding water that has evaporated.  Test your water.  Ammonia should be zero, nitrites zero, and nitrates should be safe.  You can buy these small test kits at your pet store, and they are always handy to have.  When your water chemistry is perfect, add two fish, wait one week, do a 25% water change, check your water, and if it is still free of ammonia, nitrites, and nitrates are low, add two more, and wait one week, etc.
You did not mention the size of your tank, but adding 30-35 fish at once is a big NO NO.  Adding these fish caused your ammonia level, and nitrite level to go way up.  Annonia, and Nitrites are the number one killer of fish.  They should always be zero.  One Goldfish needs at least 10 gallons of water all to himself...so 35 goldfish would need a 350 gallon tank!  It is very important that you do not overstock your tank.  Overstocked tanks, and water chemistry which is not right will kill your fish.  Ich is always present in our tanks, and it attacks stressed, or weak fish.  Overcrowding a tank will cause stress, and disease to fish.  You would never be able to keep them healthy.  The rule "one gallon per one inch of fish" is a myth.  You must calculate the size of the fish at maturity.  Some golfish, (most of them) grow very big, and need big tanks.  It is much better to have less fish, and a healthy tank.  I would also like to mention that you cannot mix goldfish with tropical fish.  If you have goldfish, then don't add any other fish but goldfish.  This too is important as fish have different needs.  They don't always mix.  Goldfish need alkaline water.  Test your PH.  It should be between 7.6-8.0  If it is low, this too will harm your fish.  To make your water alkaline, add crushed coral or sea shells.  Never use chemicals.  Add the coral, and sea shells slowly.  Put one handful in, and wait one day, check your PH.  If it is still too low, add more, wait one day, and so on until you have reached the right PH.
From what you have written me, the problem started with overstocking, poor water quality, adding too many fish at the same time, thus stressing your fish, which let to them getting ich, and dying of ammonia, and nitrite build up.  This happens very quickly.
I could help you more if you gave me the size of your tank.
I hope this will help.
Lynda