Please help! Yesterday my water had turned a poopy brown so I did a 25% water change last night. This morning its back to dark brown, Im worried about my fish. Please help with any explaination or suggestion.
Flush the toilet BEFORE taking the water out for your fish tank! (I know, that was too obvious!)
Do you have any wood in your tank? Wood releases tannins that usually turn the water a tint of brown, but if you didn't boil and rinse the wood to remove some of the tannins first, or have multiple pieces in there, you could have very dark water.
If so, take out the wood and boil it (or soak it in hot water) until the water is clear. You will have to empty the water and start with fresh water several to many times. Do water changes in your tank to clear the water.
If not, you'll have to wait for someone else to answer which is quicker than waiting for me to come up with another answer...