Its like a zombie apocalypse in my tank! Help!

Question
I'm not exactly sure how large my tank is. I believe its a 50 gallon. I have a filter, and a bubbler. No heater, no chiller. My tank stays at a steady 70 degrees though. I feed them TetraFin Floating Variety Pellets to cut down on the debre in the tank. I have currently 3 koi which are about 3 inches long and a peco catfish which is about an inch maybe.
So here is the situation. Let me stat at the beginning. Last week I bought a new baby inch and a half koi at Walmart. Here is where my big mistake was... I didn't take in consideration of the condition of the other fish when I selected my baby. They seemed to be acting strange... They would all swim around the tiny 12 inch by 12 inch thank like normal but then they would all rest on the bottom all huddled in the corner and would look almost...dead. Then suddenly they would spring to life and start swimming around again. It seemed a bit odd but I over looked it and decided to buy one anyways.
A wile after i introduced him to the tank with my other koi I started to realize that something was seriously wrong. It was like he didnt have enouph energy to get to the top and half way up he would just drift back to the bottom. he spent most of his time resting in one place at the bottom of the tank. He didnt interact with the other koi like a normal new comer koi did for me. It seemed almost ominous to me that he would spend all his time in solitude. Eventually he stopped eating. Then he went through a stage were he wouldnt leave the top of the tank and he started sitting right in from of the bubbler.. constantly. he would never leave it. He also gained this... deathly emaciated appearance. It actually kinda scared me. During this time my other fish started acting strange. they seemed like they want OUT OF THERE. one jumped out and woke me up in the middle of the night flapping around on the floor. They would race around back and forth egarly near the surface. I knew something was seriously wrong. The very same day the fish jumped out of the tank i noticed one of my other koi lost a few scales and had a strange injury on its fin. I just assumed it was as stressed as the others were feeling and it might have hit the rock display i have in the tank.
I put it off even though I had a terrible feeling in my gut.
The next morning i found the baby koi dead. I was a bit disappointed but i knew it was coming. Later i noticed my fish hadent come up to the glass and insisted on food like they were starving to death like they normally did so i went to go feed them...and i immediately saw one of my koi with one of his eyes completely white. his body seemed kinda dull and dingy and the color was slightly faded. The fish i noticed the previous day to have missing scales had lost nearly half of them by now and it had a faded look also. its eyes weren't white but they are sunken in. the third koi appears to be fine. full of energy. still has its appetite.
So currently i have all the koi in my bathtub so to get them out of the water they were in.
the 2 koi has nearly no energy. i can catch them with my hands with no effort. their scales are falling off...
I dont know whats happening and its kinda scary to see them in a state like this. they have been my beloved pets for quite some time now. I love watching them very much.
I'm assuming it has to do with a bacteria infection but of what kind? how to i manage this? will the two die? can i save the third who had no symptoms yet? i live no were near town and i have no money. is there a way i can help them at home? please help me. they look horrifying. like they are already dead but still moving.

Answer
Pennie,
WOW you have quite a bit going on. Unfortunately, you learned the hard way about a few things. It is never a good idea to buy fish from Walmart. Not sure why, but it must be the breeders they use. You also learned why it is very important to have a hospital tank. Whenever you buy new fish, you should always keep it in your hospital tank for at least 2 weeks to make sure the new fish is not ill. I always keep them in the hospital tank for 1 month.

It is not uncommon for fish to go through a "stress" period when they are first introduced to the main tank. They go through quite a lot by leaving the breeder, going to the store, being bought, and then placed in a new tank. It is a very stressful time for them. I am hoping that you intend on putting the Koi into a pond very soon. Koi should never be placed into an aquarium. Koi can grow up to 36 inches when full grown, and belong in a pond. IF you want to keep them indoors, you will eventually need to get a tank that can hold about 2,000 gallons. It is true that the size of the tank will determine the size of he fish. A small tank will stunt their growth, but only the skeletal structure of the fish. All the internal organs will continue to grow causing a very painful death.

It sounds like the new Koi had a serious illness that did not take long to attack the other fish.Since they are Koi, I would add some salt to their water. This will help keep them healthy. The ratio is 0.3%-0.5%. 0.3% equals 3lbs of salt in 100 gallons of water. It is important to remember that salt not evaporate. Once the salt is in the water, and you are just topping off the tank, do not add any more salt. The salt is added only once to the tank.

http://www.fishyou.com/freshwater/salt.html

Koi are jumpers, and when they jump it could be because of anything. Koi are Carp and we all know how they love to jump. As long as you don't have one that jumps all the time, then all is ok. Another reason could be that the ammonia or nitrite levels are elevated, or not enough oxygen in the water. If the swimming area is not large enough for them, they will jump. What are your water perimeters? Particularly the ammonia and nitrite levels. I would also check your Ph level. Sometimes Koi will jump when placed in a new home.

There are a few reasons koi will loose scales. If your fish are losing scales for no apparent reason (such as breeding) then it is commonly found to be caused from Myxosporidiosis. The only treatment for this is to keep doing water changes and get rid of the parasites. Symptoms: Fish gasping, pale gills loosing scales. Other types of parasites are Trichodina. Killing off Trichodina can be accomplished with salt in many instances. Flukes can be controlled by several methods including SupaVerm and Fluke Tabs. Follow all instructions for dosing as most fluke remedies are toxic of overdosed or left in too long. Bacteria can also cause koi to loose their scales. This needs to be treated with an antibiotic ointment.

I have included this website about Koi illnesses. I think it will help you. If after reading it, and your Koi do not have anything on the list let me know and I will try to help more.

http://www.koi-pond-guide.com/koi-diseases.html

Good Luck!!