Goldfish problems

Question
I have a 60Litre tank with filter and air pump and I usually do an entire cleanout of the tank once a month and every few weeks I do a %30 water change. 2 days ago I took my 6 goldfish out of the tank and put them into a container while I cleaned it out and when the tank was clean again I put them back in. Suddenly they started breathing rapidly and stayed at the bottom of the tank. I found it odd because I have had them for months and they have never acted this way. Two of my goldfish died and sank to the bottom of the tank. The rest of my fish have been breathing rapidly. I have two black moores, 1 nymph and a ranchu. The baby black moore is happily swimming but the rest won't move or even eat. My ranchu won't move but floats around the tank for hours. I looked at his gills and they are red but I notice fluffy white stuff on the gills. I'm not sure if they are supposed to be there or not. Have I maybe sent my goldfish into shock or have they caught a desease? I fear my goldfish won't last much longer. Every half an hour all the fish will depserately swim to the top for air and then zoom back down and stay there. Have I made an error or is it something else? Please help.

Answer
Shara,
If you have a cycled tank with a filter, why are you cleaning the whole tank? Every time you do that, you reset the filter and the tanks tries to cycle again. With goldfish, you need to do your water changes every week, not every few weeks. The fish are reacting to the complete water change. The filter and the gravel have beneficial bacteria that both the tank and the fish need to stay healthy. Every time you do a complete water change with a tank cleaning, you are removing that bacteria. If the fish are "panting", that usually indicates that there is not enough oxygen in the water. Try adding an air stone or two to the tank.

A 60 liter tank is in no way big enough for the six goldfish. That size tank is not even big enough for 1 goldfish. One goldfish should be in a tank so smaller than 76 liters and each additional fish has to have 38 liters. To house 6 goldfish, the absolute smallest tank would be 266 liters. The filter you use in that tank should be for an even larger tank. Goldfish are messy fish and need a filter that will be able to handle all the waste they produce. My suggestion is to either buy a larger tank, or pick different fish to keep. If the gills are red, the fish are suffering from ammonia and/or nitrite poisoning. Their water changes have to be done at least once a week, but since your tank is so small you should be doing your water changes no less than twice a week. Test your water daily for ammonia and nitrites. If there is a reading higher than zero, there is too much in the water and you will have to do a water change. This is the fastest way to bring down the levels. Make sure you are testing daily for both chemicals.