Mass death

Question
We have had our 12 gallon freshwater tank for only a few months and everything seemed to be going fine. I have been informed that it is normal for a few fish to die when you start a new tank so I was prepared for that but the deaths have continued beyond the first few weeks. We have(had)two catfish, one dojo, a loach and several white tip and neons.Algae began to accumulate despite our efforts to keep the tank clean so we bought two plecos (as prescribed by the fish store) and they did a marvelous job but the smaller one died two days later. I noticed its tail seemed to have been bitten because it looked shorter and shredded. Then I noticed one of the neons tail appeared to be in the same shape and his and some of the white tips colors were going dim. Its been one week since the plecos death and all the fish except for the catfish have white spots all over their bodies and a thin floaty film covering it. They all were swimming very slow and I knew something was wrong and this morning I woke up to find the dojo, and five of the smaller fish dead and the remaining fish near death. I will give a brief description of the behaviors and physical ailments that I have noticed in the fish that have died to help you understand a little better. White spots,  floaty filmy layer, increased algae production on the glass, shredded tails and loss of the ability to swim or stay at the bottom of the tank.I hope this makes some sense to you. I feel really frustrated. We are down to only the catfish who do not seem affected (yet) by any of the sickness that has been spread in the tank. I want to try and at least salvage them. Let me know if you need any more information to further assess the situation. Thank you for your time.

Answer
Hi Ada:  I was sorry to hear that your fish experience has been so bad.  It sounds like to me you have a fungus or parasite issue.  I would start to treat the tank by changing 20-30 percent of the water and adding aquarium salt.  I would also visit an aquarium store... not a pet store and tell them you want a medication for fungus... Jungle makes a great product for fungal treatments.  I would also pick up a bottle of ALGAEFIX it is safe for fish and plants and works well to get rid of algae.  The other thing I'd like for you to consider is that poor nutrition plays the biggest part in fish ailments... that and stress.  Not all fish will eat flake food... plecostomus and other cat fish need to have their diets supplemented with algae wafers.... Dojo loaches also need to have a varied diet. I feed my dojo's live tubiflex worms twice a week along with what the other fish get.  I hope this helps... keep me posted... dave