The water in my tank looks yellow and dingy

Question
I have had the aquarium for about three months.  About two weeks ago the water started looking dingy and yellow.  Last week my pictus cat died and today two of my cherry barbs died.  The cat seemed like he was doing great and his death was sudden.  The barbs have had spots on their fins for the last few days.  What should I do?  It makes me so sad when the fish die and I just want them all to be happy and healthy!

Answer
Hi Jessica:  I am sorry to read about your fish death.  I would start by getting the water chemistry check.. most fish stores will do this for your without cost.  I would also change about 50% of the water immediately and add in some beneficial bacteria.  Make sure that you clean the gravel.  If you are feeding flake food I would monitor how much you are feeding... feed only what they will eat in about 3 minutes of time.  If you have slow eater... like bettas... they chew their food forever... then make sure they are getting some extra food too... just them though.  I suspect that the ammonia levels in the tank are high and that the nitrogen cycle is in motion.  The water test will tells us if that is true or not. Do you have a heater in your tank???? let me know... dave