gold fish thin fins

Question
Hi, I just placed a large Chinese bowl at the front door with 8 gold fish as a Koi pond. It takes approx 75 to 80 liters. Unfortunately I lost 3 fish to water conditions and 2 others were very bad with red gills and curled up which are now heaps better! One  of those is constantly hungry..? The others not so mainly just hang around at the bottom or very top and barely swim. I have been to the pet shop and had the water checked 2 times and all is good... However I I am not happy. It is winter here and the water is cold. I still check the water and change it regularly once a week.  All the fins are thin as in clamped together and the fish swim using more effort.The water is a little cloudy ..?
I have started to use a bag called Nitra zorb in the filter to help reduce ammonia, nitrate and nitrite and I wash it regularly.. i put aquarium salt in the pond and use (recommended to me)on the new water ...water ager,  stress zyme,  and melafix.  Why do they have thin fins? Am i helping or hindering?
Please help my cute fish live and be happy!  :)
They have divine long fins that used to flow beautifully!
Thank you so much for donating your time to help!

Answer
Leah,

 Sorry to hear you are having problems with your fish. Your fish are suffering from Fin rot. The first thing I would do is remove all the surviving fish from the bowl and place them in a tank. Bowls are not good for any type of fish. You have goldfish, the messiest fish there is. Goldfish do not have stomachs, so everything comes out just as fast as it goes in. I would never place a tank near a door or a window. That adds to the coldness. Goldfish eat constantly, so that is why you have one that seems to always be hungry. One goldfish needs 20 gallons of water all by itself so if you want to have 8 of them your tank needs to be at least 90 gallons. Clamped fins is a parasite, and needs to be treated right away. Get some Jungle Parasite Clear and follow the directions on the label. That will clear up the fin rot. Unfortunately, you will continue to have problems as long as you keep them in a bowl. They are little fish that grow into very large fish. When you do the water changes, don't forget to treat the new water before you add it to the tank. There is chlorine and other chemicals in tap water that can be quite harmful to fish. I use Prime in all my tanks and it works very well, and knock on wood, all my fish have been very healthy. If you do the regular water changes, use a filter and feed them properly, they will become very healthy and happy. I would remove the salt from the tank since your fish do not need it all the time. It is used to help aid in the relief of some illnesses. You do not need to add a water ager. Just get a bottle of Prime and add that to your water every time you do the change. The water is cloudy most likely due to the over crowding of the tank. Also every time you clean the filter, you are causing the tank to recycle.

As far as the cold, you can add a heater to their tank, even though they don't need one. Turn it on up no higher than 77 degrees, but I think around 72 degree will be just fine.

I hope this all helps