I have a 50 gallon freshwater tank. It has 4 swordtails and 2 neon. I also have a live plant in it. I have attempted to add a pleco (purchased from petco and petsmart). They seem to do fine the first 2 or 3 days and then they die. I have a home test kit and everything seems to be in order. I have had my fish for almost a year and routinely clean my tank. There isn't a lot of residue from overfeeding but algae seems to continue to grow. Nothing is wrong with my other fish or my plant (which I keep clipping as it grows so fast). Can you give me some advise?