Hi Gajraj, I'm assuming you only have a small tank [under 20 gallons] so you overstocked it-4 fish is way too many to begin with & their pooping sent the tank into bio meltdown as the filter could not keep pace with it. The cloudy water you are seeing now is the evidence of this so stop feeding for a couple of days-the fish will be ok & after that period only feed tiny amounts in moderation.

You need to be doing partial water changes using same temperature, treated water to dilute this toxic water. Test for ammonia & nitrite-everything above zero should be considered fatal & keep on doing the water changes until you have removed the problem.

The red fins is another sign of toxic water-keep the water good & the problem will go away. Do not add any more fish or you will overload your eco system & never mix any other types of fish with Goldfish. The link below tells you all about good tnak management.