Also in my case it was this:
My soft water tank keeps a rather orange tinted lipton look though the clarity is crystal. if it gets cloudy it is always a nitrate climb at this point of the tank life.
you may want to use search for topics on "cloudy water" "red water" "pink water""milky water" and smelly water
Test Your Water with Your Nose. Good water in your fish's home has a characteristic smell. It smells very much like humus or fresh mown grass.
But water that is cloudy or foamy with the wrong particulates smells like an egg fart; fishy; like garlic or cigar smoke. Smell can be an important clue in helping to decide whether the water is good for fish or not good. If in doubt, the water each day in increments of 50% or less(depending on how old the tank os adn if you treat it for ph
changing), until the water quality looks and smells good again.