Cleaner fish keep dying

Question
Hi, I am having an issue with my 20 gallon freshwater tank. I originally set it up April the fourth of this year, originally I put too many fish in because they all died. So I got 2 Mickey mouse platys and a Pleco. Soon after putting fish in the tank I started getting brown algae all over everything in the tank including the live plants. I spoke with someone at the petstore who told me just to wipe it off the plants I thought at that time something was wrong with the plants. I did some research that told me it was common in new tanks and just had to keep up on the cleaning and it could go away with time. So the Placo ended up dying after about a week or two. So I bought an otocinclus, just one, because the pet store said one would do. Well that ended up dying after about a week. Then one of my Mickey mouse platys ended up having babies shortly there after. So I was trying to find a cleaner fish that would not eat the babies even though, originally I didn't want them to breed, so I got an upside down swimming catfish thinking a catfish would be a cleaner not thinking about the whole upside down thing. I know silly. So, the 2 babies that have survived were about 4 weeks old when I got 2 ghost shrimp and a Chinese algae eater. So come to find out Chinese algae eaters are aggressive which is not what the petstore said, he ended up killing the female Mickey mouse platy and one shrimp so I brought him back. I picked up 3 little juli Cory catfish. About a week after getting the catfish the other shrimp died. So about a week later I get 3 ghost shrimp. All the while my ammonia level is fine I have a Seachem Ammonia Alert in my tank, it does go up a small amount almost to the stress zone when something dies but that it. Now one of my juli cory catfish has died. I'm noticing that it is only anything cleaning my tank that is dying. I have kept the Mickey mouse platys, 5 with the 2 babies, and the upside down swimming catfish alive just fine. The brown algae is kind of getting better but it's not gone. I'm sorry for such a long question...but what's wrong with my tank? Please help!?

Answer
Renee,

When you set up the tank, did you cycle it before you added any fish? IF not, that is why the all the original fish died. When you buy fish, it is good to quarantine them in your hospital tank for a minimum of 2 weeks before adding them to the main tank. This way if there is something wrong with the new fish, it will come out in that time and you don't get the rest of the tank mates sick. As for why the other fish are dying it could be the water. Ammonia and nitrites have to be at zero at all times. Some fish are  more sensitive to the water conditions than others. I would not add any more fish to the tank however, because you do not want to over populate again. Also, research your fish before you get them to make sure they will be ok with the fish you already have. Unfortunately, most large pet store chains employees do not know much, if anything, about the fish they sell. I would just keep what you have for now and see how everyone does in a month or so before trying to add any more algae eaters. None of my tanks have that kind of fish because there is not enough algae, I have none, to feed them. If there is not enough you will have to supplement them with algae wafers. If algae grows, then just clean the decorations and the inside of the glass and that should help. Also, do not leave the light on more than 8 hours a day. Any longer will breed algae very quickly. Make sure you are doing your weekly water changes of 25% to help with this problem as well.