I bought 120 gallon tank and cycled it in October. When the cycle was complete I started adding batches of fish. I currently have 2 clown loaches, a syno angelicus and 8 african cichlids( 2 mbuna and the rest peacock or haps). The last batch of fish were added the first week of December so everyone has been in there awhile. 2 weeks ago I noticed my ruby red wasn't eating and two days later he died. I looked him over and could find nothing wrong looking. He just stopped eating, became sluggish and died. Then last weekend I noticed my lithobates not eating. He was acting fine and had normal energy and I did not notice anything wrong with him. I bought some garlic gaurd as I was told this can help. He has been eating for a couple days now and seems fine. Yesterday I noticed that my livingstonii Was very sluggish and basically just rested on the bottom and wouldn't really move or eat. I test my water every couple of days and it has alway been 0 ammonia and nitrite and between 10 to 20 nitrate. Ph has always been steady around 8 and temp around 80. I room some water to my lsf and they confirmed my results. I am new to fish so maybe I am missing a physical sign of what wrong so I will attach a pic. I have been doing water changes every week to week and a half. I feed them nls pellets and feed once a day and not very much, just a small pinch. I feed them peas once a week and don't feed at all once a week. I am having a huge brown algae outbreak as we'll but I don't think that is the problem. Any help hints or suggestions are appreciated.
